Copper supported catalyst comprising a Ca-deficient hydroxyapatite for waste gas NOx removal

ABSTRACT

A porous material comprises at least 60 wt % of a calcium-deficient hydroxyapatite having a Ca/P molar ratio of less than 1.67, having a specific BET surface area of at least 110 m 2 /g and a pore volume of at least 0.41 cm 3 /g, both measured after heat treatment at 120° C. A catalyst composition for catalytic reduction of NO x  compounds, comprising an active catalyst component: Cu and/or CuO deposited on the porous material as support. A deNOx process according to which an ammonia source is injected into a combustion waste gas stream containing NOx; and to which the catalyst composition is brought into contact with the waste gas stream at a temperature of at least 100° C. and preferably at most 600° C. to carry out, in the presence of O 2 , a reduction by NH 3  of at least a portion of the NOx.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. national stage entry under 35 U.S.C. § 371 of International Application No. PCT/EP2017/081819 filed Dec. 7, 2017, which claims priority benefit to U.S. provisional application No. 62/432,406 and No. 62/432,407, both filed on Dec. 7, 2016, the whole content of these applications being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention pertains to the field of selective catalytic reduction catalysts, particularly, to a copper-containing supported catalyst on a porous material comprising hydroxyapatite having high BET surface area and pore volume and to methods to using such catalyst in a process for waste gas purification treatment, particularly for the removal of nitrogen oxides (NOx) from a waste gas effluent generated by a combustion process, for example from a flue gas stream originating from a stationary combustion source.

BACKGROUND

When burning fossil fuels to produce energy, one typically uses a high temperature combustion process in the presence of air. Unfortunately, this type of process produces both nitrogen oxides (NOx), which are well-known pollutants, and other components that are harmful to health or the environment, such as carbon monoxide, sulfur oxides (SOx), volatile heavy metals, and unburned hydrocarbons. Thus, it is important to remove these materials prior to their release into the environment.

There have been many investigations into methods that allow for the removal of these substances. Combustion modifications and adsorption techniques can be used for this removal, but may suffer from limited maximum removal of pollutants such as NOx and limited capacity. A method for addressing the problem of noxious exhaust gases is catalytic removal, which by comparison, is extremely effective in removing large proportions of unwanted exhaust components and is capable of treating very large volumes of exit gases for long periods of time.

Selective catalytic reduction (SCR) has been one of the most effective technologies for removing NO (the main nitrogen oxide formed at high temperature) from a waste gas effluent originating from a stationary or mobile combustion source. Stationary combustion sources are mainly utility boilers, industrial boilers, incinerators, and cogeneration turbines. Mobile combustion sources are mainly vehicles such as automobiles, trucks.

The SCR process is widely used for example in the U.S., Japan, and Europe to reduce emissions of large utility boilers and other commercial applications. Increasingly, SCR processes are being used to reduce emissions in mobile applications such as in large diesel engines like those found on ships, diesel locomotives, automobiles and the like.

In order to effect the reduction of NOx in waste combustion gases through catalytic reduction processes, it is necessary either to introduce a reducing agent, such as ammonia, and/or to use the unburned hydrocarbons present in the waste gas effluent. The SCR process generally provides the reduction of NOx, (NO, N₂O and NO₂) species using the reducing agent (e.g., ammonia) in the presence of oxygen and a catalyst to produce molecular nitrogen and water.

Selective catalytic reduction (SCR) of NO by NH₃ as reducing agent in the presence of O₂, that causes the formation of NO₂ (from the parent NO) in the gas reagent mixture, is a complex reaction can be schematized with the following series of main reactions (I) and (II): 4NO+4NH₃+O₂→4N₂+6H₂O  (I) 2NO₂+4NH₃+O₂→3N₂+6H₂O  (II) Other common reactions that could be taken into account when low 02 concentration is present in the gas mixture are the following reactions (III) and (IV): NO+NO₂+2NH₃→2N₂+3H₂O  (III) 6NO₂+8NH₃→7N₂+12H₂O  (IV).

At temperatures around 300-350° C., competition between the reaction of NO reduction by NH₃ and the reaction of NH₃ oxidation by oxygen forming NO and/or N₂ and/or N₂O can occur, according to the following reactions (V) to (VII): 4NH₃+5O₂→4NO+6H₂O  (V) 2NH₃+2O₂→N₂O+3H₂O  (VI) 4NH₃+3O₂→2N₂+6H₂O  (VII).

These last reactions (V) to (VII) sequestrate NH₃, the reducing agent, to the SCR process: they are in competition with the previous reactions of NOx reduction. The occurrence of these reactions (V) to (VII) is responsible for the observation of a maximum of the conversion curve of the NOx species as a function of reaction temperature; that is to say, the rate of NOx (NO+NO₂) reduction is not continuously increasing with temperature because, staring from a defined temperature, the concentration of the reducing agent (NH₃) decreases due to its oxidation by oxygen.

The SCR process is a competitive reaction scheme constituted by series of parallel reactions, the kinetics of each reaction and its dependence on temperature has to be exploited in order to selectively obtain NO reduction by ammonia and to avoid ammonia oxidation by oxygen. Finding a catalytic system to selectively obtain NO reduction by ammonia in a large temperature interval is thus challenging.

Various catalysts have been used in the SCR processes. Catalysts, including various metals, transition metal oxides, and mixed metal oxides have been employed for NO reduction. Initial catalysts, which employed platinum or platinum group metals, were found unsatisfactory because of the need to operate in a temperature range in which explosive ammonium nitrate forms. In response to environmental regulations in Japan, the first vanadium/titanium SCR catalyst was developed, which has proven to be highly successful. Further development has resulted in the development of vanadium catalyst deposited on titanium oxide/tungsten oxide support material.

Metal-promoted zeolite catalysts including, among others, iron-promoted and copper-promoted zeolite catalysts, for the selective catalytic reduction of nitrogen oxides with ammonia are known.

Zeolites are aluminosilicate crystalline materials having rather uniform pore sizes which, depending upon the type of zeolite and the type and amount of cations included in the zeolite lattice, range from about 3 to 10 Angstroms in diameter.

Chabazite (CHA) is a small pore zeolite with 8 member-ring pore openings (^(˜)3.8 Angstroms) accessible through its 3-dimensional porosity. A cage like structure results from the connection of double six-ring building units by 4 rings. WO 2008/106519 discloses a catalyst comprising: a zeolite having the CHA crystal structure and a mole ratio of silica to alumina greater than 15 and an atomic ratio of copper to aluminum exceeding 0.25. The catalyst is prepared via copper exchanging NH₄ ⁺-form CHA with copper sulfate or copper acetate. The copper concentration of the aqueous copper sulfate ion-exchange step varies from 0.025 to 1 molar, where multiple copper ion-exchange steps are needed to attain target copper loadings. U.S. Pat. No. 8,293,199 describes processes for the preparation of copper containing molecular sieves with the CHA structure having a silica to alumina mole ratio greater than about 10, wherein the copper exchange step is conducted via wet state exchange and prior to the coating step and wherein in the copper exchange step a liquid copper solution is used wherein the concentration of copper is in the range of about 0.001 to about 0.25 molar using copper acetate and/or an ammoniacal solution of copper ions as copper source.

Acidic zeolites such as copper ion-exchanged Y zeolites, H mordenite, and Cu—H mordenite have been reported to be efficient catalysts for NO reduction by NH3, particularly for the high-temperature application of SCR technology—see for example, Choi et al, Journal of Catalysis (1996) vol. 161, pages 597-604; Putluru et al, Applied Catal. B: Environmental (2011) vol. 101, pages 183-188.

Iron-promoted zeolite beta (U.S. Pat. No. 4,961,917) has been an effective commercial catalyst for the selective reduction of nitrogen oxides with ammonia.

Unfortunately, it has been found that under harsh hydrothermal conditions, for example exhibited during regeneration of a soot filter with temperatures locally exceeding 700° C., the activity of many metal-promoted zeolites begins to decline. This decline is often attributed to dealumination of the zeolite and the consequent loss of metal-containing active centers within the zeolite.

The catalysts employed in the SCR process ideally should be able to retain good catalytic activity over the wide range of temperature conditions of use, for example, from 200° C. to 600° C. or higher, preferably under hydrothermal conditions since water is generated during NOx reduction (see reactions (I) and (II) above). Hydrothermal conditions are also encountered in practice, such as during the regeneration of a soot filter, a component of the exhaust gas treatment system used for the removal of particles.

Despite the various catalysts being developed such as the zeolite supported catalysts, there exists a need for lower cost catalysts that provide and maintain high catalytic activity in the SCR reaction, especially for once-through applications in which the catalyst is injected into a waste gas stream and where the contact time between the supported catalyst and NOx may be short in the order of a second to a few minutes.

SUMMARY OF INVENTION

An embodiment of the present invention relates to a porous material comprising at least 60 wt % of a calcium-deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67.

The porous material may have a particularly high BET specific surface area (at least 110 m²/g) and/or a particularly high pore volume (at least 0.41 cm³/g) measured after heat treatment of the porous support at 120° C.

The porous material may have a BET specific surface area measured after heat treatment at 200° C. of at least 120 m²/g and/or at most 160 m²/g.

The porous material may have a BET specific surface area measured after heat treatment at 400° C. of at least 60 m²/g and/or at most 100 m²/g.

The porous material may have a pore volume measured after heat treatment at 200° C. of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g.

The porous material may serve as a porous support for a supported catalyst.

The porous material or support may further comprise calcium carbonate in an amount of less than 20 wt % and more than 0 wt %, preferably from 1 wt % to 19 wt %, more preferably from 2 wt % to 18 wt %, even more preferably from 5 wt % to 15 wt %, yet even more preferably from 7 wt % to 13 wt %, most preferably from 8 wt % to 12 wt %.

The porous material or support may further comprise less than 1 wt % of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt % calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt % calcium dihydroxide Ca(OH)₂, even more preferably less than 0.2 wt % calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

The porous material or support may further comprise water in an amount of less than 20 wt % and more than 0 wt %, preferably from 1 wt % to 18 wt %, more preferably from 2 wt % to 15 wt %, even more preferably from 4 wt % to 12 wt %, yet even more preferably from 5 wt % to 11 wt % most preferably from 6 wt % to 11 wt %.

The porous material or support may comprise a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 1.67 or more, more preferably of 1.68 or more.

The porous material may comprise a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite.

The porous material or support may comprise at least 65 wt %, preferably at least 70 wt %, more preferably at least 75 wt %, yet more preferably at least 80 wt %, yet most preferably at least 85 wt %, of the calcium-deficient hydroxyapatite,

and/or

at most 99 wt %, preferably at most 98 wt %, more preferably at most 97 wt %, yet more preferably at most 95 wt %, even more preferably at most 93 wt %, most preferably at most 91 wt % of the calcium-deficient hydroxyapatite.

The porous material or support may have a pore volume measured after heat treatment at 400° C. of at least 0.50 cm³/g, preferably of at least 0.60 cm³/g and/or of at most 1 cm³/g.

Another embodiment of the present invention relates to a catalyst composition for catalytic reduction of NO_(x) compounds, comprising an active catalyst component deposited on the porous material used as porous support for the catalyst;

wherein said active catalyst component comprises copper, copper oxide, or combination thereof; and

wherein said porous support comprises at least 60 wt % of a calcium-deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67.

In preferred embodiments, the porous support has a specific BET surface area of at least 110 m²/g and a pore volume of at least 0.41 cm³/g both measured after heat treatment at 120° C., or a specific BET surface area of at least 110 m²/g and a pore volume of at least 0.5 cm³/g both measured after heat treatment at 200° C.

The active catalyst component may comprise

-   -   at least 0.1 wt %, preferably at least 0.5 wt %, more preferably         at least 1.0 wt %, most preferably at least 1.5 wt %, of copper,         copper oxide, or combination thereof;

and/or

-   -   at most 15 wt %, preferably at most, more preferably at most 13         wt %, yet more preferably at most 12 wt %, most preferably at         most 11 wt %, of copper, copper oxide, or combination thereof.

The active catalyst component may be deposited on the porous support by ion exchange or impregnation.

The active catalyst component may be deposited on the porous support using a copper precursor selected from the group consisting of copper nitrate, copper acetate, copper chloride, copper acetylacetonate, and any mixture thereof.

The catalyst may be subjected to a heat treatment using a temperature from 105° C. up to 500° C., prior to being used as a catalyst.

The catalyst composition may have a BET specific surface area measured after being calcined at 400° C. of at least 65 m²/g and/or at most 100 m²/g.

The catalyst composition may have a pore volume measured after being calcined at 400° C. of:

-   -   at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or     -   at most 1.1 cm³/g, preferably of at most 1.0 cm³/g, more         preferably of at most 0.9 cm³/g. most preferably of at most 0.8         cm³/g.

Another embodiment of the present invention relates to a process for treating a waste gas stream containing nitrogen oxides (NOx), said gas stream originating from a combustion process, in which an ammonia source is injected into the waste gas stream; and in which the catalyst composition according to any embodiments of the present invention is brought into contact with the waste gas stream containing ammonia at a temperature of at least 100° C. and preferably at most 600° C. to carry out, in the presence of O₂, a reduction by NH₃ of at least a portion of the NOx to N₂ and water.

In the process, the waste gas stream temperature is at least 105° C., or at least 120° C., or at least 150° C., or at least 180° C., or at least 200° C.; and/or at most 550° C., or at most 500° C., or at most 450° C., or at most 400° C., or at most 350° C., or at most 325° C., or at most 300° C.

In the process, the catalyst composition is injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst.

The porous material or support disclosed herein comprises a Ca-deficient hydroxyapatite useful for the deposition of the active metallic component(s) of the catalytic composition.

The porous material or support generally comprises or at least 60 percent by weight (wt %), or at least 65 wt %, or at least 70 wt %, or at least 75 wt % percent by weight of the calcium-deficient hydroxyapatite.

The porous material or support may consist of or consist essentially of at least one calcium-deficient hydroxyapatite, as described herein.

The calcium-deficient hydroxyapatite is generally in the present invention in crystalline form or in vitreous form.

In preferred embodiments, the porous material or support may further include one or more additional components different from the calcium-deficient hydroxyapatite.

In an advantageous embodiment of the invention, the porous material or support is obtained or may be obtainable by the process of any items 1 to 16 of this patent application described herein below.

The porous material or support may be a material according to any items 17 to 30 of this patent application described herein below.

The porous material or support is advantageously a material according to any items 31 to 44 of this patent application described herein below.

The catalyst containing the active metallic component on the porous material or support is advantageously a material according to any items 45 to 55 of this patent application described herein below.

In another embodiment of the invention, it is particularly advantageous that the catalyst according to any of the embodiments presented herein comprising is brought into contact with a waste gas stream containing nitrogen oxides (NOx).

The porous material or support may be used in the form of a wet solid (D′), or a pulverulent solid (D″), preferably a pulverulent solid (D″), when the support particles are loaded with copper.

An advantage of the present invention is that the porous material or support used in the catalyst according to the invention, presents when in dried powder (as pulverulent solid) an improved flowability and dispersion ability in gas streams compared to previous calcium phosphate material of prior art (in particular the ones described in WO 2008/095921 from SOLVAY, using a gel step during the manufacture of the support).

BRIEF DESCRIPTION OF DRAWING

FIG. 1 illustrates the conversion of NO and NH₃ over a hydroxyapatite-based support over the range of temperature 120-450° C. in a NH₃-SCR reaction test.

FIG. 2 illustrates the conversion of NO and NH₃ and the percent of production of N₂ over the range of temperature in a NH₃-SCR reaction test 120-400° C. for a hydroxyapatite-based Cu-exchanged catalyst with about 1.5 wt % Cu.

FIG. 3 illustrates the conversion of NO and NH3 and the percent of production of N₂ over the range of temperature 120-400° C. in a NH₃-SCR reaction test for a hydroxyapatite-based Cu-exchanged catalyst with about 11 wt % Cu.

FIG. 4 reports the comparative results for the deNOx activity at temperature of 250° C. of the 7 Cu-catalysts prepared by ionic exchange with Cu-loading on hydroxyapatite support from 1.7 to 11.1 wt. % Cu.

FIG. 5 reports the comparative results for the deNOx activity at temperature of 350° C. of the same 7 Cu-catalysts prepared by ionic exchange as used in FIG. 4.

FIG. 6 reports the comparative results for the deNOx activity at temperature of 250° C. of the 5 Cu-catalysts prepared by impregnation with Cu-loading (2.1<Cu (wt. %)<10.1) on hydroxyapatite-containing support.

FIG. 7 reports the comparative results for the deNOx activity at temperature of 350° C. of the same 5 Cu-catalysts prepared by impregnation as used in FIG. 6.

FIG. 8 shows that copper on the support is needed for the deNOx activity at low temperatures (150-300° C.) and that impregnation seems a better preparation method than the ionic exchange method when copper acetate is used as Cu-precursor.

FIG. 9 illustrates the conversion of NOx over 3 hydroxyapatite-based Cu-catalysts made by ionic exchange and from 3 different copper precursors over the range of temperature 120-400° C. in a NH₃-SCR reaction test.

DEFINITIONS

Unless otherwise specified, all reference to percentage (%) herein refers to percent by weight.

As used herein, the terms “% by weight”, “wt %”, “wt. %”, “weight percentage”, or “percentage by weight” are used interchangeably.

The terms “catalyst support,” “support particles,” or “porous support” are intended to have their standard meaning in the art and refer to a porous material in the form of particles comprising a hydroxyapatite structure on the surface of which an active metal component can be deposited.

The terms “active metal catalyst” or “active component” refer to the active component deposited on support material that catalyzes the reduction of NOx compounds.

The term “catalyst” is intended to have its standard meaning in the art and refers to the combination of the active metal catalyst supported on the catalyst support particles.

“Fresh” catalyst denotes a material which has not been in contact with NOx, whereas “spent” catalyst denotes a material which has already been in contact with NOx.

As used herein, the term “upstream” refers to a position situated in the opposite direction from that in which the gas stream to be treated flows.

As used herein, the term “downstream” refers to a position situated in the same direction from that in which the gas stream to be treated flows.

In the present specification, the choice of an element from a group of elements also explicitly describes:

-   -   the choice of two or the choice of several elements from the         group,     -   the choice of an element from a subgroup of elements consisting         of the group of elements from which one or more elements have         been removed.

In addition, it should be understood that the elements and/or the characteristics of a composition, a method, a process or a use, described in the present specification, can be combined in all ways possible with the other elements and/or characteristics of the composition, method, process, or use, explicitly or implicitly, this being without departing from the context of the present specification.

In the passages of the present specification that will follow, various embodiments or items of implementation are defined in greater detail. Each embodiment or item of implementation thus defined can be combined with another embodiment or with another item of implementation, this being for each mode or item unless otherwise indicated or clearly incompatible when the range of the same parameter of value is not connected. In particular, any variant indicated as being preferred or advantageous can be combined with another variant or with the other variants indicated as being preferred or advantageous.

In the present specification, the description of a range of values for a variable, defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments in which the variable is chosen, respectively, within the value range: excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit.

In the present specification, the description of several successive ranges of values for the same variable also comprises the description of embodiments where the variable is chosen in any other intermediate range included in the successive ranges. Thus, for example, when it is indicated that “the magnitude X is generally at least 10, advantageously at least 15”, the present description also describes the embodiment where: “the magnitude X is at least 11”, or also the embodiment where: “the magnitude X is at least 13.74”, etc.; 11 or 13.74 being values included between 10 and 15.

The term “comprising” includes “consisting essentially of” and also “consisting of”.

In the present specification, the use of “a” in the singular also comprises the plural (“some”), and vice versa, unless the context clearly indicates the contrary. By way of example, “a mineral” denotes one mineral or more than one mineral.

If the term “approximately” is used before a quantitative value, this corresponds to a variation of ±10% of the nominal quantitative value, unless otherwise indicated.

DETAILED DESCRIPTION OF INVENTION

Porous Material or Support

In the text of the application, the “porous material” may be referred to as the “calcium phosphate porous support” or “porous support”; these terms can be used interchangeably.

The porous material or support used in the catalyst of the present invention preferably consists of particles. In some embodiments, the mean diameter D50 of the porous support is greater than 10 μm, in general greater than 20 μm, or even greater than 50 μm. However, this mean diameter of the porous support is in general preferably less than 200 μm, or even less than 150 μm. This makes it possible to limit the stirring powers to prevent the particles of the porous support from needing high velocities of waste gases to be treated at the injection points of the catalyst for the treatment of the waste gases.

Moreover the porous material or support may have a particularly high BET specific surface area (at least 110 m²/g) measured after treatment of the porous support at 120° C.

The porous material or support may have a particularly high pore volume (at least 0.41 cm³/g) measured after heat treatment of the porous support at 120° C.

Particularly, the porous material or support may have a high adsorption capacity of metals, in particular of copper.

In particular embodiments, the porous support has a BET specific surface area measured after heat treatment at 200° C. of at least 120 m²/g and/or at most 160 m²/g.

In particular embodiments, the porous material or support has a BET specific surface area measured after heat treatment at 600° C. of at least 20 m²/g and/or at most 40 m²/g.

In particular embodiments, the porous material or support has a pore volume measured after heat treatment at 200° C. of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g.

In particular embodiments, the porous material or support has a pore volume measured after heat treatment at 600° C. of at least 0.42 cm³/g, preferably of at least 0.44 cm³/g and/or at most 0.8 cm³/g, preferably of at most 0.75 cm³/g.

For comparison, natural apatites found in Moroco for instance have specific surface areas of about 16 m²/g. Synthetic hydroxyapatites made by Dalahay's group at the Ecole Nationale Superieure de Montpellier, France, have specific BET surface areas of

-   -   about 26 m²/g (Tounsi et al, Applied Catalysis B: Environmental,         2011, vol. 107, pages 158-163); and     -   about 44 m²/g (Jemal et al, Reac. Kinet. Mech. Cat, 2013, vol.         109, pages 159-165).

In Jemal et al, Reac. Kinet. Mech. Cat, 2013, vol. 109, pages 159-165, a synthetic hydroxyapatite made using an aqueous medium had a BET about 35 m²/g and a pore volume of 0.4 cm³/g, while another synthetic hydroxyapatite made using an ethanol-water medium had a BET about 72 m²/g and a pore volume of 0.34 cm³/g.

The porous material or support should comprise at least 60 wt % of a calcium-deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67.

It is preferred that the calcium-deficient hydroxyapatite has a calcium to phosphate molar ratio (Ca/P) of more than 1.5 and less than 1.67.

In particular embodiments, the porous material or support comprises at least 65 wt %, preferably at least 70 wt %, more preferably at least 75 wt %, yet more preferably at least 80 wt %, yet most preferably at least 85 wt %, of the calcium-deficient hydroxyapatite.

In particular embodiments, the porous material or support comprises at most 99 wt %, preferably at most 98 wt %, more preferably at most 97 wt %, yet more preferably at most 95 wt %, even more preferably at most 93 wt %, most preferably at most 91 wt % of the calcium-deficient hydroxyapatite.

In particular embodiments, the porous material or support may comprise a Ca/P molar ratio of 1.60 or more, preferably more than 1.62, more preferably more than 1.65.

In some embodiments, the porous material or support may comprise a Ca/P molar ratio of 1.60 or more, preferably of 1.62 or more, more preferably of 1.65 or more, even more preferably of 1.67 or more, most preferably of 1.68 or more.

The porous support particles are preferably composed of calcium phosphate, the structure of which is intermediate between tricalcium phosphate and calcium phosphate hydroxyapatite. These particles then evolve very rapidly towards an apatite structure. The particles of the porous material or support preferably contain a calcium-deficient hydroxyapatite structure having a calcium to phosphate molar ratio (Ca/P) of less than 1.67. It is preferred that the calcium-deficient hydroxyapatite has a calcium to phosphate molar ratio (Ca/P) of more than 1.5 and less than 1.67.

Such porous material or support particles are composed on their surface of plate-like crystallites, of thickness of a few nano-meters (nm).

Particles of calcium phosphate porous material or porous support may be covered with plate-like crystallites, having a thickness of at most 25 nm, preferably of at most 20 nm, more preferably of at most 10 nm. The thickness of plate-like crystallites may be at least 1 nm, preferably at least 2 nm, more preferably at least 4 nm.

The porous material or support used in the present invention may further have a remarkably low solubility of the phosphates contained in the porous support particles.

The particles of the calcium phosphate porous material or support used in the catalyst of the present invention in general comprise at least 60 wt % calcium phosphate, and advantageously still at least 65 wt % calcium phosphate.

The particles of the calcium phosphate porous material or support may further comprise: water, of the order of from 0 to 20 wt %, advantageously from 3% to 20 wt %, more advantageously from 5 wt % to 20 wt %; calcium carbonate from 0 to 20 wt %, advantageously from 1 wt % to 25 wt %, more advantageously from 5 wt % to 20 wt %.

In some embodiments, the particles of the calcium phosphate porous material or support may further comprise calcium carbonate in an amount of less than 20 wt % and more than 0 wt %, preferably from 1 wt % to 19 wt %, more preferably from 2 wt % to 18 wt %, even preferably from 5 wt % to 15 wt %, yet even more preferably from 7 wt % to 13 wt %, most preferably from 8 wt % to 12 wt %.

The particles of the calcium phosphate porous material or support may further comprise: water, of the order of from 0 to 20 wt %, advantageously from 3% to 20 wt %, more advantageously from 5 wt % to 20 wt %; calcium carbonate from 0 to 20 wt %, advantageously from 1 wt % to 25 wt %, more advantageously from 5 wt % to 20 wt %.

The particles of the calcium phosphate porous material or support may further comprise calcium dihydroxide from 0 to 20%, advantageously from 0% to 4%, or more advantageously from 0 to 1 wt %. In some embodiments, the porous material or support may comprise less than 1 wt % of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt % calcium dihydroxide, more preferably less than 0.3 wt % calcium dihydroxide, even more preferably less than 0.2 wt % calcium dihydroxide. In some embodiments, the porous material or support is substantially free of calcium dihydroxide (i.e., less than 0.1 wt % Ca(OH)₂).

The particles of calcium phosphate porous material or support may additionally contain residual compounds originating from the use of the raw materials in the method of making it, such as: CaCl₂, Ca(NO₃)₂, sands or clays; these constituents are in general less than 5 wt %, advantageously less than 2 wt %.

The term “apatite” denotes a family of mineral compounds, the chemical formula of which can be written in the following general form: Me₁₀(XO₄)₆Y₂

In this formula, Me generally represents a divalent cation (Me²⁺), XO₄ a trivalent anionic group (XO₄ ³⁻) and Y a monovalent anion (Y⁻).

Calcium phosphate hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ crystallizes in the space group of the hexagonal system. This structure consists of a close-packed quasi-hexagonal stack of XO₄ groups, forming two types of parallel tunnels.

The existence of these tunnels gives apatites chemical properties akin to those of zeolites. Vacancies may also be created either by the departure of anions and cations, or by the presence of cations or anions of different valency. Apatites therefore appear to be particularly stable structures which may tolerate large gaps in their composition.

Hydroxyapatite should not be confused with tricalcium phosphate (TCP), which has a similar weight composition: Ca₃(PO₄)₂. The Ca/P molar ratio of TCP is 1.5 whereas the Ca/P molar ratio is 1.67 for hydroxyapatite. Industrial apatites sold as food additives or mineral fillers are, as a general rule, variable mixtures of TCP and hydroxyapatite.

The present hydroxyapatite in the porous material or support is deficient in calcium compared to a hydroxyapatite with a Ca/P molar ratio of 1.67. The Ca/P molar ratio of the calcium-deficient hydroxyapatite is preferably more than 1.5 and less than 1.67.

Calcium may be and is preferably present in another form (other than the calcium-deficient hydroxyapatite) in the porous material or support. Calcium carbonate is generally present in the porous material or support. The weight ratio of the calcium-deficient hydroxyapatite to calcium carbonate is generally equal to or greater than 3, preferably equal to or greater than 4, more preferably equal to or greater than 5, yet more preferably greater than 7, most preferably equal to or greater than 9.

Generally, because of that other form of Ca in the porous material or support, the porous support generally has a higher Ca/P molar ratio than the calcium-deficient hydroxyapatite present in the porous support. For that reason, even though the calcium-deficient hydroxyapatite in the porous material or support may have a Ca/P molar ratio less than 1.67, the entire porous support may have a Ca/P molar ratio equal to or more than 1.67. In preferred embodiments, the calcium-deficient hydroxyapatite in the porous material or support may have a Ca/P molar ratio of about 1.55-1.59, while the porous material or support may have a Ca/P molar ratio of about 1.60-1.67.

Other salts of calcium and phosphate, including TCP, do not have the same properties as hydroxyapatite or a hydroxyapatite like structure. Although TCP can also react with metals, a hydroxyapatite of Ca/P=1.67 as well as a calcium-deficient hydroxyapatite (Ca/P<1.67) are more advantageous as they can enclose metals in the form of an insoluble, and therefore relatively inert, matrix.

In some preferred embodiments, the porous material or support in the catalyst composition is substantially free of carbon, i.e., less than 0.5 wt % of carbon.

In some other embodiments, the porous material or support in the catalyst composition may comprise carbon for example in an amount of at least 0.5 wt % carbon but in an amount of less than 7 wt % carbon, preferably less than 6 wt % carbon, more preferably less than 5 wt % carbon or less than 4 wt % carbon.

In some preferred embodiments, the porous material or support in the catalyst composition is substantially free of bone char. “Bone char” (also called “bone charcoal”) refers to a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made. Bones (especially cow bones) are heated in a sealed vessel at up to 700° C. (1,292° F.); a low concentration of oxygen is maintained during heating, as oxygen content affects the quality of the bone char product, particularly its adsorption capacity. Most of the organic material in the bones is driven off by heat. Bone char generally contains 7-10% carbon.

Method for Making the Porous Material to be Used as Catalyst Support

The process for producing the calcium phosphate porous material or support may comprise:

-   -   in a first step, use is made of a source of calcium and a source         of phosphate ions in water, in a molar ratio that is adjusted so         as to obtain a Ca/P molar ratio of between 0.5 and 1.6, and the         source of calcium is reacted with the phosphate ions at a pH of         between 2 and 8, in order to obtain a suspension (A) of calcium         phosphate, and     -   in a second step, added to the suspension (A) are an alkaline         compound comprising hydroxide ions in order to set a pH of more         than 8, preferably of at least 8.5, and an additional source of         calcium in order to obtain a suspension (B) of calcium phosphate         porous support having a Ca/P molar ratio of more than 1.6.

In the process of manufacture, the source of calcium to make the porous material or support advantageously comprises calcium carbonate, or calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate. The source of calcium is more advantageously a limestone, or a mixture of limestone and calcium oxide or hydroxide. More advantageously, the source of calcium is in the form of powder or aqueous suspension of powder and the powder is selected from the group consisting of: calcium carbonate, calcium oxide, calcium hydroxide, and a mixture thereof, and the powder for the source of calcium has a mean particle size of less than 300 μm.

It is advantageous for the source of calcium selected from the group consisting of: calcium carbonate, calcium oxide, calcium hydroxide, and mixtures thereof to be in the form of a powder or aqueous suspension of powder, and to have a small particle size. In one recommended variant, the mean diameter of the particles of the powder for the calcium source is less than 300 μm, advantageously less than 200 μm and preferably less than 100 μm. The mean diameter in question is the D50, that is to say the diameter such that 50% by weight of the particles have a diameter less than said value.

In the process of manufacture, various sources of phosphate ions to make the porous material or support may be used, in particular:

-   -   phosphoric acid,     -   or a dihydrogen phosphate salt such as a sodium, potassium or         ammonium dihydrogen phosphate salt, preferably a sodium         dihydrogen phosphate salt,     -   or a monohydrogen phosphate salt such as a sodium, potassium or         ammonium monohydrogen phosphate salt, preferably a sodium         monohydrogen phosphate salt.

In the process of manufacture to make the porous material or support, phosphoric acid is preferred due to its greater availability and lower cost compared to dihydrogen and monohydrogen phosphate salts.

In the process of manufacture to make the porous material or support, in the first step the Ca/P molar ratio is in particular:

-   -   between 0.50 and 1.35, preferably between 0.70 and 1.30,     -   or: between 1.4 and 1.6, preferably between 1.4 and 1.5.

During the first step where calcium and phosphate are used in a Ca/P molar ratio of between 0.5 and 1.6 and where they are reacted at a pH between 2 and 8, the compounds formed in the suspension (A) are a mixture of monocalcium phosphate (MCP) having the weight formula Ca(H₂PO₄)₂, of dicalcium phosphate (DCP) having the weight formula CaHPO₄, or the hydrate thereof, brushite, having the weight formula CaHPO₄.2H₂O, and of octacalcium having the weight formula Ca₈H₂(PO₄)₆.6.5H₂O. The Ca/P molar ratios are respectively for these compounds: 0.5 (MCP), 1.0 (DCP and brushite), 1.33 (octacalcium).

In order to promote, in the first step, the formation of MCP and DCP, a Ca/P ratio of between 0.50 and 1.35, preferably between 0.7 and 1.30, is favored. This Ca/P molar ratio is particularly advantageous when the source of calcium from the first step comprises calcium carbonate, and the source of phosphate is phosphoric acid (H₃PO₄) or is a dihydrogen phosphate salt such as a sodium or potassium or ammonium salt. Specifically, this makes it possible to obtain a rapid attack of the calcium carbonate and a rapid degassing of the CO₂. In addition to calcium carbonate, the source of calcium may comprise calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

In order to promote, in the first step, the formation of DCP and octacalcium, a Ca/P ratio of between 1.4 and 1.6, preferably between 1.4 and 1.5, is favored. This molar ratio is advantageous when use is made of a source of calcium having less than 30% by weight of carbonate, such as preferably: calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

In the method of manufacture to make the porous material or support, in the first step, the source of calcium and the phosphate ions are in general reacted for at least 0.1 hour, preferably at least 0.5 hour. It is not useful to react them over excessively long periods of time. Advantageously, the source of calcium and the phosphate ions are reacted for at most 4 hours, more advantageously at most 2 hours, or even at most 1 hour. For example, a time period of 1 hour at pH 5 already enables a good reaction of the calcium and the phosphate ions, and makes it possible to sufficiently release the CO₂ when a source of calcium comprising calcium carbonate is used, before moving on to the second step.

In the method of manufacture to make the porous material or support, in the second step, the suspension (B) of calcium phosphate porous material or support in general has a Ca/P molar ratio of at most 5, preferably of at most 3, more preferably still of at most 2.

In the method of manufacture to make the porous material or support, it is advantageous, in the second step, for the alkaline compound used, that comprises hydroxide ions, to be sodium hydroxide and/or calcium hydroxide.

In the method of manufacture to make the porous material or support, it is particularly advantageous for the additional source of calcium to be selected from the group consisting of calcium chloride, calcium nitrate, and calcium acetate, preferably calcium chloride, and for this additional source of calcium to be added to the alkaline compound, in order to finely adjust the Ca/P molar ratio and in order to limit the concentration of phosphorus element in the aqueous solution (C) of the suspension (B) to at most 5 mmol, advantageously to at most 0.5 mmol, more advantageously to at most 0.05 mmol of phosphorus element per liter of the aqueous solution (C). Specifically, this makes it possible, coupled with the use of hydroxide ions for setting the pH of the second step, to limit the losses of phosphates in the process water.

In the method of manufacture to make the porous material or support, in general, the stirring speed rate and the density of the suspension, in the second step and advantageously also in the first step, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 200 cps. The viscosity of the porous material or support suspension (B) in the second step of the process of the present invention is typically about 10 cps (mPa·s). Specifically, the production of a gel, even in the presence of the second step, results in making porous material or support particles of small particle size, with weight-mean D50 values of less than 10 μm, which may be a disadvantage for certain applications.

The suspended solids density of the suspension (A) in the first step is in general at most 20 wt %. The suspended solids density of the suspension (B) in the second step is in general at most 15 wt %. The suspended solids density of the suspension (A) and/or of the suspension (B) is advantageously at least 5 wt %, more advantageously at least 7 wt %, most advantageously at least 10 wt %. It has been indeed observed that a too low density of the suspension decreases the efficacy of the produced porous material or support particles in metal adsorption (in particular on Cu). Moreover a too low density of the suspension induces longer time of water separation when decantation or filtration is used in the method of making the porous material or support.

In the method of manufacture to make the porous material or support, the stirring speed of the suspension during the first and second steps corresponds generally to a stirring dissipated energy in the reactors volume of at least 0.2 kW/m³ and at most 1.5 kW/m³, preferably at least 0.5 kW/m³ and at most 1.0 kW/m³.

In a first embodiment of the method of manufacturing the material or support, the first step is carried out at a temperature of less than 50° C., preferably at most 45° C., or at most 40° C. This low-temperature first step makes it possible to obtain a calcium phosphate porous material or support at the end of the second step in the form of particles of large to medium particle size and having a high specific surface area. The method may manufacture in particular particles of porous material or support by this first embodiment, comprising at least 60% by weight of hydroxyapatite or hydroxyapatite-like structure, and having a mean size of at least 30 μm, preferably of at least 50 μm and having a specific BET surface area and/or pore volume as described above. In some embodiments, the specific BET surface area measured after heat treatment at 200° C. is at least 110 m²/g.

In some embodiments, the porous support may comprise at least 2 wt %, preferably at least 2.5 wt % or at least 3 wt %, more preferably at least 5 wt %, and yet more preferably at least 6 wt % of hydroxide ions.

In some embodiments, the porous support may comprise from 2 wt % to 6 wt % of hydroxide ions, preferably from 2.5 wt % to 5 wt % of hydroxide ions.

In a second embodiment of the method for manufacturing the porous material or support, the first step is carried out at a temperature of at least 50° C., preferably of at least 55° C., or of at least 60° C. This makes it possible to obtain a porous material or support in the second step in the form of particles of small particle size and having a lower specific surface area. The process may manufacture in particular particles of porous material or support obtained by the method according to this second embodiment, comprising at least 60% by weight of hydroxyapatite, and having a mean size of at most 30 μm, preferably of at most 20 μm. In some embodiments, particles of porous material or support have a specific BET surface area of at least 15 m²/g, preferably of at least 50 m²/g, and having a content of hydroxide ions of greater than 2% by weight, preferably greater than 3.5% by weight, and more preferably greater than 4% by weight.

In the first or second embodiment of the method of manufacture, it is advantageous for the second step to be carried out at a temperature of at least 45° C., preferably of at least 55° C., or of at least 60° C., or of at least 80° C. Specifically, this makes it possible to rapidly convert the calcium phosphate compounds from the first step into the calcium phosphate porous material or support, with a good fixation of the hydroxide ions at the core and at the surface of the calcium phosphate porous material or support, and to more rapidly consume the phosphates from the solution of the suspension (B). Advantageously, the second step of the manufacture method is carried out at a temperature of at least 45° C., preferably of at least 55° C., or of at least 60° C., or of at least 80° C., for a time period of at least 0.1 to 0.5 hour. In general, the addition of the alkaline compound comprising hydroxide ions in order to set the pH of the second step, and of the additional source of calcium in order to obtain a suspension (B) of calcium phosphate porous material or support having a Ca/P molar ratio of greater than 1.6 last no more than 4 hours, advantageously no more than 2.5 hours: at higher temperature such as at 50° C. or at 60° C. generally one hour is sufficient, as at 40° C. the alkaline compound addition to set the pH of the second step is generally longer: and about 2.5 hours are needed. Preferably, the alkaline compound addition is stopped when the pH remains at the set value for at least 15 minutes. Advantageously, once the additions of hydroxide ions for setting the pH of the second step, and the addition of the additional source of calcium are completed, the suspension (B) is left to cool for 1 to 24 hours, preferably at least 10 hours, down to ambient temperature. This makes it possible to mature the calcium phosphate porous material or support and to reduce the residues of MCP/DCP or brushite, or of octacalcium (precipitated during the first step), into a hydroxyapatite structure and into calcium phosphate and calcium hydroxide complexes, within the suspension (B).

Optionally, in the manufacture method, at the end of the second step, the suspension (B) comprises an aqueous solution (C) and calcium phosphate porous material or support particles, and

-   -   in a third step, a portion of the aqueous solution (C) is         separated from the suspension (B) in order to obtain an aqueous         suspension (D) comprising at least 18% and at most 50% of         calcium phosphate porous material or support particles, or in         order to obtain a wet solid (D′) comprising at least 50% and at         most 80% of calcium phosphate porous material or support         particles, or a pulverulent solid (D″) comprising at least 80%         and at most 95% of calcium phosphate porous material or support         particles and at least 5% and at most 20% of water.

In some embodiments, the porous material or support material is not isolated from the aqueous solution in which it is suspended prior to deposition of the active catalyst component.

In alternate embodiment, the porous support material may be isolated prior to deposition of the active catalyst component. Preferably in this instance, greater than 90% or 95% by weight of the solvent or dispersion medium is removed. More preferably, greater than 98% of the medium is removed. The isolation may comprise any type of solid/liquid separation; filtration is a preferred isolation technique.

In some embodiments, the porous material or support material may not be subjected to drying prior to deposition of the active catalyst component.

In alternate embodiment, the porous material or support material may be dried prior to deposition of the active catalyst component. Drying is preferably carried out after the porous material or support material has been isolated. When water is the dispersion medium, a suitable drying temperature is about 80° C. to about 120° C. However, it will be apparent to one of skill in the art that lower or higher drying temperatures may be used. For example, drying temperatures of less than 80° C. may be used if the drying time is increased or the drying pressure is decreased. A preferred drying temperature is from about 100° C. to about 120° C.

Copper-Containing Supported Catalyst

The calcium phosphate porous material obtained by the manufacture method described herein may be effective for use as a porous support for a catalyst for treating a waste gas contaminated by nitrogen oxides, in particular a flue gas contaminated by NOx and originating from a combustion process.

One or more embodiments of the present invention pertains to a catalyst supported on the calcium phosphate porous material or support as described previously.

A particular embodiment of the present invention pertains to a catalyst composition for catalytic reduction of NO_(x) compounds, comprising an active catalyst component deposited on the porous material or support; wherein the active catalyst component comprises copper, copper oxide, or combination thereof.

The active catalyst component may comprise at least 0.1 wt %, preferably at least 0.5 wt %, more preferably at least 1.0 wt %, most preferably at least 1.5 wt %, of copper, copper oxide, or combination thereof; and/or may comprise at most 15 wt %, preferably at most at most 13 wt %, more preferably at most 12 wt %, most preferably at most 11 wt %, of copper, copper oxide, or combination thereof. A range of from 1.5 wt % to 11 wt % of Cu and/or CuO is particularly suitable. A range of from 3 wt % to 8 wt % of Cu and/or CuO is also particularly suitable.

In particular embodiments, the catalyst composition has a BET specific surface area measured after being calcined at 400° C. of at least 65 m²/g and/or at most 100 m²/g.

In particular embodiments, the catalyst composition has a pore volume measured after being calcined at 400° C. of at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or at most 1.1 cm³/g, preferably of at most 1.0 cm³/g, more preferably of at most 0.9 cm³/g, most preferably of at most 0.8 cm³/g.

In particular embodiments, the catalyst composition has an average pore radius measured after being calcined at 400° C. of at least 5 nm, preferably at least 7 nm, and/or at most 30 nm, preferably at most 25 nm. The average pore radius is preferably determined from Gurvich rule: rp=2 (Vp/SBET) 10³, where Vp is the pore volume in cm³/g, SBET is the BET surface area in m²/g, and the pore radius is in nm.

In particular embodiments, the catalyst composition has a microporous and mesoporous morphology.

In some embodiments, the catalyst composition contains not more than 50%, preferably not more than 40%, of the copper species in the oxide form (CuO).

In alternate embodiments, the catalyst composition contains more than 50%, preferably more than 70%, of the copper species in the oxide form (CuO).

Method of Making the Copper-Containing Supported Catalyst

The active catalyst component may be deposited on the porous material or support using a solution of a copper precursor. Hereinafter, concerning the catalyst, when the porous material is used as a catalyst support, reference will be made to the “porous support”.

A preferred copper precursor may be selected from the group consisting of copper nitrate (CuNO₃), copper acetate (Cu(Ac)), copper chloride (CuCl₂), copper acetylacetonate (Cu(Acac)), and any mixture thereof.

The active catalyst component may be deposited on the porous material or support by wet impregnation or ion-exchange, preferably by ion-exchange.

Wet impregnation (with small amount of excess water solution) is a catalyst preparation technique that does not require a copper precursor with ionic character. Therefore, also copper acetylacetonate besides copper acetate can be used as Cu precursor for the catalyst preparation via impregnation.

Impregnation is a technique in which a new phase is added on the external surface and in the pores of the porous material or support (if the pore dimensions allow the entrance of the used Cu precursor). In the case of the hydroxyapatite containing porous material or support, Cu besides Ca will be present in the final catalyst composition.

Ionic exchange (or ion-exchange or ion exchange, used interchangeably) is a technique for modifying the surface composition of materials that have metal cations bound to the framework with electrostatic bonds. This preparation technique necessitates a Cu precursor with ionic character. Therefore, copper acetate, copper chloride, and copper nitrate can be selected as copper precursor to provide Cu²⁺ cations. Copper chloride and copper nitrate are particularly suitable as copper precursor with the ion exchange method.

The new cations are introduced in the sample composition and they substitute the original cations of the sample (in this case Cu²⁺ cations substitute Ca²⁺ cations of the hydroxyapatite which enter into solution). Ionic exchange is a method that exploits the electrostatic interaction between the added cations (Cu²⁺) and the negative framework of the starting material (hydroxyapatite).

Concerning the possibility to load the porous support material with a given desired amount of the added metal, there are differences among the two preparation methods.

By impregnation, it is possible to load the support with a given amount of impregnating phase which has been chosen “a priori”. The preparation technique does not employ any filtration or separation step of the impregnated support sample from the solution that contains the metal precursor of the loading phase. So, all the desired amount of metal precursor can effectively be loaded on the support.

By ion exchange, it is not possible to load the support exactly with a desired amount of any cation. Once the exchange reaction has finished, filtration has to be performed to separate the exchanged solid from the copper precursor solution that may contain some residual amount of the Cu²⁺ cations.

After depositing the active catalyst component on the porous support, the particles may be washed to remove the non-exchanged or excess active component species. Washing medium may comprise water (such as deionized water) or a solvent similar to the one used to dissolve or disperse the copper precursor(s).

After the deposition of the active catalyst component on the porous support and the optional washing, the particles may be isolated by any suitable means, such as filtration, to remove the medium/solvent into which the copper precursor is dissolved or suspended or to remove the washing medium at the end of the washing step. Preferably, greater than 90% or 95% of the medium is removed. More preferably, greater than 98% of the medium is removed.

In some embodiments, after the deposition of the copper precursor onto the support, the (isolated) catalyst particles may be subjected to a heat treatment. The heat treatment may use a temperature from 105° C. to 500° C.

In some embodiments, after the deposition of the copper precursor onto the support, the resulting (isolated) catalyst particles may be subjected to a heat treatment (drying). The temperature at which the particles are dried is dependent on the solvent medium and the pressure which is used to dry the particles. Drying typically uses a temperature of 180° C. or less. Drying is typically carried out in air or in an O₂-containing atmosphere which may comprise another gaseous component such as nitrogen gas (N₂), helium or combination thereof. Drying may be carried out in a vacuum or not.

Typically, the same drying temperatures and times described above for drying the porous support will be useful for drying the supported catalyst after the active metal component has been deposited. The moisture level of the dried supported catalyst can be measured by standard methods known in the art to determine if the material has been dried for a sufficient amount of time at the particular temperature. When water is the medium into which the copper precursor is dissolved or suspended, a suitable drying temperature is about 80° C. to about 120° C. However, it will be apparent to one of skill in the art that lower or higher drying temperatures may be used. For example, drying temperatures of less than 80° C. may be used if the drying time is increased or the drying pressure is decreased. A preferred drying temperature is from about 100° C. to about 120° C. Usually, the catalyst is dried for at least 10 hours at 100-120° C. to ensure that the solvent is adequately removed. More typically, the catalyst may be dried for at least 12, 14 or 16 hours at 100-120° C. to ensure that the solvent is removed to a sufficient level.

In some embodiments, after the deposition of the copper precursor onto the support, the catalyst is subjected to a heat treatment (calcining) using a temperature more than 180° C. and up to 500° C. Preferably, calcining is performed after a drying step, but not necessarily.

In some embodiments, after the deposition of the copper precursor, the catalyst is not subjected to a heat treatment using a temperature greater than 180° C. (no calcination), prior to being used as a catalyst.

Use of the Supported Catalyst

Consequently, another aspect of the present invention also relates to the use of the supported catalyst for the purification of a waste gas.

A particular embodiment of the present invention relates to a DeNOx process according to which an ammonia source is injected into a combustion waste gas stream containing NOx; and according to which the catalyst composition is brought into contact with the waste gas stream at a temperature of at least 100° C. and preferably at most 600° C. to carry out, in the presence of O₂, a reduction by NH₃ of at least a portion of the NOx.

In the treatment process according to the invention, the catalyst particles are contacted with the waste gas stream for a sufficient time so that the catalyst converts by reduction by NH₃ at least a portion of the NOx.

Preferably, the particulate catalyst is used with the waste gas stream in a contact reactor such as packed in a fixed bed or fluidized in a fluidized bed, or is injected in a duct/pipe/conduit through which the waste gas stream flows. The fluidization gas to maintain the catalyst particles suspended in the fluidized bed may comprise or consist of the waste gas stream to be treated.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst to provide contact of the catalyst with the waste gas. If the catalyst is dispersed into the waste gas to be treated, the resulting mixture is subjected to a separation in order to produce a treated gas which is partially purified of NOx and a spent catalyst that is removed from the treated gas.

In the treatment process according to the invention, the waste gas stream may be a flue gas stream containing at least NOx. The catalyst supported on the porous support particles may be contacted with the flue gas stream being at a temperature of at least 100° C., or of at least 150° C., or of at least 180° C., or of at least 200° C., the resulting mixture then being subjected to a separation in order to obtain a resulting solid and a flue gas stream partially purified of NOx. The flue gas stream may be at a temperature of at most 800° C., or of at most 600° C., of at most 550° C., or of at most 500° C.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be packed into a fixed bed in order for the waste gas stream passes through the bed of the catalyst to provide contact of the catalyst with the waste gas.

In some embodiment of the process for treating a waste gas stream containing NOx, the catalyst composition may be fluidized in a fluidized bed to provide contact of the catalyst with the waste gas. The fluidization gas to maintain the catalyst particles suspended in the fluidized bed may comprise or consist of the waste gas stream to be treated.

When the catalyst is injected as a powder into a flue gas stream flowing through a flue duct, its use may be once-through—that is to say, the catalyst is not used again. The contact time between the particulate catalyst and the flue gas stream to be treated may be very short in the order of millisecond(s) to seconds, such as at least one millisecond (ms), advantageously at least 5 ms, more advantageously at least 10 ms and/or at most 5 seconds, even more advantageously at most 4 seconds, yet even more advantageously at most 3 seconds.

When the catalyst is packed or fluidized in a contact reactor, its use may be more long term—that is to say, the catalyst bed, whether fixed or fluidized, is used for a period of time greater than one week or even several months. The contact time between the particulate catalyst and the waste gas effluent to be treated may be in the order of millisecond(s) to seconds, such as at least one millisecond (ms), advantageously at least 5 ms, more advantageously at least 10 ms and/or at most 3 seconds, even more advantageously at most 2 seconds, yet even more advantageously at most 1 second.

The effectiveness of the treatment of NOx may be monitored by comparing the concentrations of NOx upstream (in the waste gas stream) and downstream of the treatment (in the partially treated gas stream), for example by an automatic analyser or by sampling and analysis.

For a deNOx application which is not once-through, the supported catalyst charge of a SCR contact reactor may be in general regularly renewed in portions, for example, by partial purging of the spent catalyst which has been in contact with NOx, and by adding fresh supported catalyst to the contact reactor. “Fresh” catalyst denotes a material which has not been in contact with NOx, whereas “spent” catalyst denotes a material which has already been in contact with NOx. Such a process thus may ensure a replenishment of the catalyst activity when the catalyst may suffer from some catalytic deactivation after contact with the waste gas stream and reaction with NOx.

In particular, the present invention relates to the following embodiments:

Item 1. Process for producing a calcium phosphate porous support, according to which:

-   -   in a first step, use is made of a source of calcium and a source         of phosphate ions in water, in a molar ratio that is adjusted so         as to obtain a Ca/P molar ratio of between 0.5 and 1.6, and the         source of calcium is reacted with the phosphate ions at a pH of         between 2 and 8, in order to obtain a suspension (A) of calcium         phosphate, and     -   in a second step, added to the suspension (A) are an alkaline         compound comprising hydroxide ions in order to set a pH of more         than 8, preferably of more than 8.5, preferably of at least 9,         or of at least 10, and an additional source of calcium in order         to obtain a suspension (B) of calcium phosphate porous support         having a Ca/P molar ratio of more than 1.6.

Item 2. Process according to the preceding item, in which in the second step the pH is set between 8 and 10.5, preferably between 8.5 and 10.

Item 3. Process according to any one of the preceding items, in which the source of calcium comprises calcium carbonate, or calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

Item 4. Process according to any one of the preceding items, in which the source of phosphate ions is phosphoric acid.

Item 5. Process according to any one of items 1 to 3, in which the source of phosphate ions is a dihydrogen phosphate salt such as a sodium, potassium or ammonium dihydrogen phosphate salt, preferably a sodium dihydrogen phosphate salt.

Item 6. Process according to any one of items 1 to 3, in which the source of phosphate ions is a monohydrogen phosphate salt such as a sodium, potassium or ammonium monohydrogen phosphate salt, preferably a sodium monohydrogen phosphate.

Item 7. Process according to any one of the preceding items, wherein in the second step, the suspension (B) of calcium phosphate porous support has a Ca/P molar ratio of at most 5, preferably of at most 3, more preferably still of at most 2.

Item 8. Process according to any one of the preceding items, in which, in the first step, the Ca/P molar ratio is:

between 0.50 and 1.35, preferably between 0.70 to 1.30,

or: between 1.4 and 1.6, preferably between 1.4 and 1.5.

Item 9. Process according to any one of the preceding items, wherein the source of calcium is in the form of powder or aqueous suspension of powder and the powder is selected from: calcium carbonate, calcium oxide, calcium hydroxide, or a mixture thereof, and the powder has a mean particle size of less than 300 μm.

Item 10. Process according to any one of the preceding items, in which the stirring speed and the density of suspension, in the second step and advantageously also in the first step, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 100 cps or at least 200 cps.

Item 11. Process according to any one of the preceding items, in which, in the second step, the alkaline compound used that comprises hydroxide ions is sodium hydroxide and/or calcium hydroxide and/or magnesium hydroxide.

Item 12. Process according to any one of the preceding items, in which, in the second step, the additional source of calcium is selected from calcium chloride, calcium nitrate, or calcium acetate, preferably calcium chloride, and is added in addition to the alkaline compound, in order to finely adjust the Ca/P molar ratio and limit the concentration of phosphorus element in the aqueous solution (C) of the suspension (B) to at most 5 mmol, advantageously to at most 0.5 mmol, more advantageously to at most 0.05 mmol of phosphorus element per litre of aqueous solution (C).

Item 13. Process according to any one of the preceding items, in which the first step is carried out at a temperature of less than 50° C., preferably of at most 45° C., more preferably of at most 40° C.

Item 14. Process according to any one of items 1 to 12, in which the first step is carried out at a temperature of at least 50° C., preferably of at least 55° C., more preferably of at least 60° C.

Item 15. Process according to any one of the preceding items, in which the second step is carried out at a temperature of at least 40° C., preferably of at least 45° C., more preferably of at least 55° C., even more preferably of at least 60° C., or of at least 80° C.

Item 16. Process according to any one of the preceding items wherein at the end of the second step, the suspension (B) comprises an aqueous solution (C) and calcium phosphate porous support particles, and

-   -   in a third step, a portion of the aqueous solution (C) is         separated from the suspension (B) in order to obtain an aqueous         suspension (D) comprising at least 18% and at most 50% of         calcium phosphate porous support particles, or to obtain a wet         solid (D′) comprising at least 50% and at most 80% of calcium         phosphate porous support particles, or to obtain a pulverulent         solid (D″) comprising at least 80% and at most 95% of calcium         phosphate porous support particles and at least 5% and at most         20% of water.

Item 17. Particles of calcium phosphate porous support obtainable by the process according to item 13, comprising at least 60% by weight of hydroxyapatite, and having a mean size of at least 30 μm.

Item 18. Particles of calcium phosphate porous support according to the preceding item comprising at least 70%, preferably at least 75%, more preferably at least 80% by weight of hydroxyapatite.

Item 19. Particles of calcium phosphate porous support according to Items 17 or 18 having a mean size of at least 50 μm.

Item 20. Particles of calcium phosphate porous support according to items 17 to 19 having a specific surface area of at least 50 m²/g, more preferably of at least 110 m²/g, even more preferably of at least 120 m²/g, or of at least 140 m²/g, or at least 160 m²/g.

Item 21. Particles of calcium phosphate porous support according to Items 17 or 19 having a mean size of at most 200 μm, preferably of at most 100 μm, more preferably of at most 70 μm.

Item 22. Particles of calcium phosphate porous support according to items 17 to 21 comprising at least 2%, preferably at least 5%, and more preferably at least 6% by weight of hydroxide ions.

Item 23. Particles of calcium phosphate porous support according to items 17 to 22 covered with plate-like crystallites, and wherein the plate-like crystallites have a thickness of at most 25 nm, preferably of at most 20 nm, more preferably of at most 10 nm.

Item 24. Particles of calcium phosphate porous support according to item 23 wherein the thickness of plate-like crystallites is at least 1 nm, preferably at least 2 nm, more preferably at least 4 nm.

Item 25. Particles of calcium phosphate porous support according to Items 17 to 24 and having a mean size of at least 50 μm.

Item 26. Particles of calcium phosphate porous support according to Items 17 to 25 wherein the solubilized phosphate of 10 g of such particles stirred in 90 mL of water during 24 hours with a lab magnetic barrel, then filtrated on a 0.45 μm nitrocellulose membrane, is less than 10 mg PO₄/L of water.

Item 27. Aqueous suspension (D) comprising at least 25% and at most 50% by weight of calcium phosphate porous support particles according to item 17 to 26, preferably obtainable from the process of item 16.

Item 28. A pulverulent solid (D″) comprising at least 80 wt % and at most 95 wt % of the calcium phosphate porous support particles according to item 17 to 26 and comprising at least 5 wt %, preferably at least 6 wt %, more preferably at least 10 wt %, even more preferably at least 15 wt % of water, advantageously obtainable from the process of item 16.

Item 29. A pulverulent solid (D″) according to item 28 comprising at most 20 wt % of water.

Item 30. Particles of calcium phosphate porous support obtainable by the process according to item 14, comprising at least 60% by weight of hydroxyapatite, and having a mean size of at most 30 μm, preferably of at most 20 μm and having a specific surface area of at least 15 m²/g, preferably of at least 50 m²/g, and having a content of hydroxide ions of greater than 2% by weight, preferably greater than 3.5% by weight, and more preferably greater than 4% by weight.

Item 31. A porous material or support comprises at least 60 wt % of a calcium-deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, preferably more than 1.5 and less than 1.67; the porous support having a specific BET surface area measured after heat treatment at 120° C. of at least 110 m²/g and a pore volume measured after heat treatment at 120° C. of at least 0.41 cm³/g; or having a specific BET surface area measured after heat treatment at 200° C. of at least 110 m²/g and a pore volume measured after heat treatment at 200° C. of at least 0.5 cm³/g.

Item 32. The porous material or support according to Item 31, further comprising calcium carbonate in an amount of less than 20 wt % and more than 0 wt %, preferably from 1 wt % to 19 wt %, more preferably from 2 wt % to 18 wt %, even more preferably from 5 wt % to 15 wt %, yet even more preferably from 7 wt % to 13 wt %, most preferably from 8 wt % to 12 wt %.

Item 33. The porous material or support according to Item 31 or 32, comprising less than 1 wt % of calcium dihydroxide Ca(OH)₂, preferably less than 0.5 wt % calcium dihydroxide Ca(OH)₂, more preferably less than 0.3 wt % calcium dihydroxide Ca(OH)₂, even more preferably less than 0.2 wt % calcium dihydroxide Ca(OH)₂, most preferably being substantially free of calcium dihydroxide Ca(OH)₂.

Item 34. The porous material or support according to any of the items 31 to 33, further comprising water in an amount of less than 20 wt % and more than 0 wt %, preferably from 1 wt % to 18 wt %, more preferably from 2 wt % to 15 wt %, even more preferably from 4 wt % to 12 wt %, yet even more preferably from 5 wt % to 11 wt % most preferably from 6 wt % to 11 wt %.

Item 35. The porous material or support according to any of the Items 31 to 34, comprising a Ca/P molar ratio of 1.60 or more, preferably of 1.65 or more, preferably of 1.67 or more, more preferably of 1.68 or more.

Item 36. The porous material or support according to any of the Items 31 to 35, comprising a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite.

Item 37. The porous material or support according to any of the Items 31 to 36, comprising at least 65 wt %, preferably at least 70 wt %, more preferably at least 75 wt %, yet more preferably at least 80 wt %, yet most preferably at least 85 wt %, of the calcium-deficient hydroxyapatite,

Item 38. The porous material or support according to any of the Items 31 to 37, comprising at most 99 wt %, preferably at most 98 wt %, more preferably at most 97 wt %, yet more preferably at most 95 wt %, even more preferably at most 93 wt %, most preferably at most 91 wt % of the calcium-deficient hydroxyapatite.

Item 39. The porous material or support according to any of the Items 31 to 38, having a BET specific surface area measured after heat treatment at 200° C. of at least 120 m²/g and/or at most 160 m²/g.

Item 40. The porous material or support according to any of the Items 31 to 39, having a BET specific surface area measured after heat treatment at 400° C. of at least 60 m²/g and/or at most 100 m²/g.

Item 41. The porous material or support according to any of the Items 31 to 40, having a BET specific surface area measured after heat treatment at 600° C. of at least 20 m²/g and/or at most 40 m²/g.

Item 42. The porous material or support according to any of the Items 31 to 41, having a pore volume measured after heat treatment at 200° C. of at least 0.55 cm³/g, preferably of at least 0.55 cm³/g and/or at most 1.0 cm³/g, preferably of at most 0.95 cm³/g.

Item 43. The porous material or support according to any of the Items 31 to 42, having a pore volume measured after heat treatment at 400° C. of at least 0.50 cm³/g, preferably of at least 0.60 cm³/g and/or at most 1 cm³/g.

Item 44. The porous material or support according to any of the Items 31 to 43, having a pore volume measured after heat treatment at 600° C. of at least 0.42 cm³/g, preferably of at least 0.44 cm³/g, and/or at most 0.8 cm³/g, preferably of at most 0.75 cm³/g.

Item 45. A catalyst composition for catalytic reduction of NO_(x) compounds, comprising an active catalyst component deposited on the porous material or support of any of the Items 31 to 44, wherein said active catalyst component comprises copper, copper oxide, or combination thereof.

Item 46. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the preceding Item 45, according to which the active catalyst component comprises

-   -   at least 0.1 wt %, preferably at least 0.5 wt %, more preferably         at least 1.0 wt %, most preferably at least 1.5 wt %, of copper,         copper oxide, or combination thereof;

and/or

-   -   at most 15 wt %, preferably at most, more preferably at most 13         wt %, yet more preferably at most 12 wt %, most preferably at         most 11 wt %, of copper, copper oxide, or combination thereof.

Item 47. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-46, according to which the active catalyst component is deposited on the porous support by ion exchange.

Item 48. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-47, according to which the active catalyst component is deposited on the porous support using a copper precursor selected from the group consisting of copper nitrate, copper acetate, copper chloride, copper acetylacetonate, and any mixture thereof.

Item 49. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-48, which is subjected to a heat treatment using a temperature from 105° C. up to 500° C., prior to being used as a catalyst.

Item 50. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-49, which is not subjected to a heat treatment using a temperature greater than 200° C., prior to being used as a catalyst for catalytic reduction of NO_(x) compounds.

Item 51. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-50, in which the catalyst composition has a BET specific surface area measured after being calcined at 400° C. of at least 65 m²/g and/or at most 100 m²/g.

Item 52. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-51, in which the catalyst composition has a pore volume measured after being calcined at 400° C. of:

-   -   at least 0.3 cm³/g, preferably of at least 0.41 cm³/g, and/or     -   at most 1.1 cm³/g, preferably of at most 1.0 cm³/g, more         preferably of at most 0.9 cm³/g. most preferably of at most 0.8         cm³/g.

Item 53. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-52, having a microporous and mesoporous morphology.

Item 54. The catalyst composition for catalytic reduction of NO_(x) compounds according to any of the Items 45-53, in which the catalyst composition has an average pore radius measured after being calcined at 400° C. of at least 5 nm, or at least 7 nm, and/or at most 30 nm, or at most 25 nm, preferably wherein the average pore radius is determined from Gurvitch rule: rp=2 (Vp/SBET) 10³, where Vp is the pore volume in cm³/g, SBET is the BET surface area in m²/g, and the pore radius is in nm.

Item 55. A catalyst composition for catalytic reduction of NO_(x) compounds, comprising an active catalyst component deposited on the particles of the calcium phosphate porous support according to any of the Items 17 to 26 or Item 30, or of the pulverulent solid (D″) according to Item 28 or 29, wherein the active catalyst component comprises copper, copper oxide, or combination thereof.

Item 56. Process for treating a waste gas stream containing nitrogen oxides (NOx), said gas stream originating from a combustion process, in which an ammonia source is injected into the waste gas stream; and in which the catalyst composition according to any of the Items 45-55 is brought into contact with the waste gas stream containing ammonia at a temperature of at least 100° C. and preferably at most 600° C. to carry out, in the presence of O₂, a reduction by NH₃ of at least a portion of the NOx to N₂ and water.

Item 57. Process according to item 56 in which the waste gas stream temperature is:

-   -   at least 105° C., or at least 120° C., or at least 150° C., or         at least 180° C., or at least 200° C.; and/or     -   at most 550° C., or at most 500° C., or at most 450° C., or at         most 400° C., or at most 350° C., or at most 325° C., or at most         300° C.

Item 58. Process according to Item 56 or 57 in which the catalyst composition is injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst.

The disclosure of all patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.

Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.

Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present specification to the extent that it might render a term unclear, the present specification shall take precedence.

Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of systems and methods are possible and are within the scope of the invention.

Accordingly, the scope of protection is not limited by the description and Examples set out below, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.

The present invention having been generally described, the following Examples are given as particular embodiments of the invention and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims to follow in any manner.

EXAMPLES Example 1—Preparation of Calcium Phosphate Porous Material to Serve as Catalyst Support

In this example, three calcium phosphate (Ca/P) supports labelled S12, S14, S16 were made under similar conditions as those described in example 1 (particularly in examples 1b and 1c) of WO2015/173437 patent application. The differences in conditions are explained below. After synthesis, the support samples were filtered and these wet samples were subjected to several analysis.

The calcium phosphate (Ca/P) support S12 was prepared in similar conditions as the ones of example 1b of WO2015/173437. Limestone was dispersed in water at 20-25° C. in a baffled 200-liter reactor. For the first step, H₃PO₄ (75%) was then added to this suspension and the mixture was stirred at 390 rpm using a double 4-blade impeller. At the end of the addition of acid, the mixture was heated up to about 50° C., and a 25 wt % suspension of Ca(OH)₂ was added to maintain the pH of the suspension at 8-8.8 for the second step. The reaction time was 140 minutes. After the reaction time, the suspension is continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25° C. The final density of solid suspension in aqueous suspension (B) was 18% by weight (solid weight reported to total weight of the aqueous suspension).

The calcium phosphate (Ca/P) support S14 was prepared in similar conditions as the ones of example 1c of WO2015/173437. Limestone was dispersed in water at 20-25° C. in a 5-liter reactor (without baffle). For the first step, H₃PO₄ (75%) was then added to this suspension and the mixture was stirred at 700 rpm using a 4-blade impeller. At the end of the addition of acid, the mixture was heated up to about 50° C., and a 25 wt % suspension of Ca(OH)₂ was added to maintain the pH of the suspension at 8.2-8.7 for the second step. The reaction time was 145 minutes. After the reaction time, the suspension is continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25° C. The final density of solid suspension in aqueous suspension (B) was 5% by weight (solid weight reported to total weight of the aqueous suspension).

The calcium phosphate (Ca/P) support S16 was prepared in similar conditions as the ones of example 1b of WO2015/173437. Limestone was dispersed in water at 20-25° C. in a 5-liter reactor (without baffle). For the first step, H₃PO₄ (75%) was then added to this suspension and the mixture was stirred at 320 rpm using a double 4-blade impeller. At the end of the addition of acid, the mixture was heated up to about 50° C., and a 25 wt % suspension of Ca(OH)₂ was added to maintain the pH of the suspension at 8.1-8.9 for the second step. The reaction time was 175 minutes. After the reaction time, the suspension is continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25° C. The final density of solid suspension in aqueous suspension (B) was 18% by weight (solid weight reported to total weight of the aqueous suspension).

1a. Porosity and Particle Size after Drying of the Support Samples S12, S14, S16

The porosity characteristics were determined after a heat treatment at 110° C. under vacuum overnight (about 16 hours). The BET specific surface area was determined by gas adsorption on a Micromeritics ASAP2020 machine. Before the analysis, the samples (0.7 to 1 g) are pretreated under vacuum at 110° C. until a stable vacuum of 4-5 μbar has been achieved. The measurements were carried out using nitrogen as adsorbent gas at 77° K via the volumetric method, according to the ISO 9277: 2010 standard (Determination of the specific surface area of solids by gas adsorption—BET method). The BET specific surface area was calculated in a relative pressure (P/PO) range varying from around 0.05 to 0.20.

The mean particles size D50 was also measured. The mean diameter D50 is the diameter such that 50% by weight of the particles have a diameter less than said value. The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 μm) and on Mie scattering theory (particles less than 10 μm), the particles being considered to be spherical.

The results can be found in TABLE 1.

TABLE 1 Samples Av Pore Volume Av. Pore size No BET* (m²/g) (cm³/g) (nm) D50 (μm) S12 166 0.45 8.9 26 S14 181 0.59 9.5 21 S16 166 0.56 9 73 *after thermal treatment at 110° C. under vacuum overnight

1b. Thermal Treatment (200-600° C.) of the Support Samples S12, S14, S16

Ageing of the three support samples at several temperatures (from 200° C. up to 600° C.) for 8 hours was carried out, in order to observe morphological changes of the samples as a function of temperature to check their thermal stability. The supports containing the hydroxyapatite will need to work in a wide temperature range (up to 600° C.) to be effective support for a deNOx catalyst.

Description of Method:

Around 10 g of the support samples (S12, S14, and S16) were put in ceramic crucibles and put in the electrical oven (Nabertherm, Germany, with temperature/time controller B-180). The thermal treatments were done in an air atmosphere under the following temperature program: from room temperature to the final temperature at 1° C./min and maintenance of the final temperature for a defined time of 8 hours. The resulting samples have been labelled with a code, which indicates the Temperature and time of the treatment (SXX/Temp./time): S12/200/8, S12/400/8, S12/600/8; S14/200/8, S14/400/8, S14/600/8, and S16/200/8, S16/400/8, S16/600/8.

The specific surface area (computed by the linear BET equation) and porosity (pore volume, pore size and pore size distribution) have been determined by N₂ adsorption/desorption isotherms collected at −196° C. using an automatic analyzer of surface area on a Sorptomatic 1900 instrument, Italy. From the Slope and Intercept of the obtained line, the volume of N₂ adsorbed on the surface in a monolayer (VM) and CBET constant have been calculated.

Pore size distribution (PSD) was computed by Barrett-Joyner-Halenda (BJH) model equation from the desorption branch of the collected isotherms and average pore size (rav,p, pore radius in nm or in Å) was calculated by the classical Gurvitch's rule: rav,p(Å)=(2Vp/SBET)10⁴ rav,p(nm)=(2Vp/SBET)10³

where Vp is the pore volume in cm³/g, SBET is the BET surface area in m²/g, and the pore radius is in A or nm (1 Å=0.1 nm).

Prior to the analysis, the wet hydroxyapatite samples and the thermally treated samples (from 0.15 to 0.30 g) have been outgassed at 150° C. for 4 hours under vacuum.

From the results obtained (adsorption-desorption isotherms and pore-size distribution), the morphology of both the S12 and S14 samples changed with temperature. This is an expected phenomenon: sintering of solids with temperature is observed on (almost) all the solids.

Sintering causes loss of surface, decrease of pore volume and of pore size. In particular, the small pores disappear and large porosity appeared. The new porosity can be also associated with inter-particle voids. This is due to the decrease of the pore volume that results in the formation of larger volume (void) among the solid particles.

Concerning S12 and S14 support samples, surface area values started from an average value of surface area around 100 m²/g and then decrease down to values of 20 m²/g following thermal treatment at 600° C. Pore Size Distribution of the two samples was centered around 2-3 nm of pore radius (for low temperature of treatment) and it increased and became very broader for high temperatures of treatment.

Concerning S16 support sample, starting from an average value of surface area of 120 m²/g, values of 30 m²/g have been observed following thermal treatment at 600° C. PSD of the sample is centered around 2 nm of pore radius (for low temperature of treatment) and it increases and become very broader for high temperatures of treatment.

Almost linear decreasing trend can be observed starting from 200° C. of thermal treatment for S12 and S14, while S16 follows a different trend. In the temperature range from 200° C. to 400° C., the decrease of surface area in S16 is limited, as well as the loss of pore volume (see TABLE 2).

TABLE 2 Pore Pore Avg pore Temp. VM vol.^(c) radius^(d) radius^(e) PSD (° C.) sample (Ncm³/g) CBET BET^(b) (cm³/g) (nm) (nm) (A) S12   110 ^(a) 166 ^(a)  200 S12/200/8 25.88 −138 112.6  0.814 2 -; 2.5  14 Broad 400 S12/400/8 15.50 −65.4 67.5 0.636 1.5; 4   19 Very broad 600 S12/600/8 4.583 −31.5 20   0.441 2.5; 11  44 Extremely broad S14   110 ^(a) 177   200 S14/200/8 31.28 −223 136.2  0.560  2; 3.5 8 Broad 400 S14/400/8 20.04 −128 87.3 0.992 1.5; 5; 8 23 Very broad 600 S14/600/8 5.710 −38.8 24.9 0.512 2; 11 40 Extremely broad S16   110 ^(a) 162   200 S16/200/8 27.50 −171 120   0.9 1.5; 2.5  15 Broad 400 S16/400/8 21.30 −110 92.8 0.690 1.5; 5   15 Very broad 600 S16/600/8 6.88 −34.7 30   0.705 2; 18 47 Extremely broad ^(a) determined after heat treatment at 110° C. under vacuum overnight (see Section 1a) ^(b)determined from 2-parameters BET equation ^(c)determined at P/Po = 0.999 ^(d)observed from PSD (by BJH model from desorption branch of the isotherm) ^(e)determined from Gurvich-rule: rp (nm) = (2 Vp/SBET) · 10³ with Vp in cm³/g and SBET in m²/g

1c. Evaluation of the Water Content

The wet support samples (S12, S14, and S16) have been weighed in ceramic crucibles (ca. 10 g with precision on an analytical scale). The crucibles were put into an oven (Heraeus Instruments, Germany, vacutherm) overnight (ca. 16 h) at 120° C. in static dry air atmosphere. After cooling to room temperature in a dryer, the crucibles were weighed again on an analytical scale.

The following losses of mass, corresponding to water desorption, were obtained and are shown in TABLE 3.

1d. Temperature Programmed Desorption of Water by TGA/DTGA

The wet samples (S12, S14, and S16) were put on the plate of the thermobalance (ca. 15 mg). The following three-step program on a TGA 7 PerkinElmer thermal analyzer was applied entirely done under N₂ flowing: i) isothermal step at 35° C. for 2 min; ii) heating from 35° C. to 800° C., at controlled rate (10° C./min); iii) cooling from 800° C. to 50° C. A calibration of the temperature was performed by measuring the Curie transitions (TC) of high-purity reference materials (alumel, nickel, perkalloy, and iron: TC of 163°, 354°, 596°, and 780° C., respectively) at the same heating rate (b) employed for this analysis. For each sample, three analyses were carried out to check the reproducibility of the obtained results.

Total amount of water desorbed in the temperature interval 35° C.-800° C. are shown in TABLE 3. The determined values are in agreement with those evaluated from the simple mass determinations after treatment at 120° C. (see paragraph: 1c. Evaluation of water content). This indicates that the samples did not contain any impurity derived from the synthetic method.

1e. Temperature of Water Desorption:

The water desorption began almost at room temperature or little higher (at the starting of the TGA analysis, 35° C.) and it ended at the following temperatures: 105° C., 112° C., and 103° C. for S12, S14, and S16, respectively (evaluated by computing the end of the desorption process on the DTGA curve). The maximum rate of water desorption was observed at the following temperatures (Tmax) are shown in TABLE 3. After the phenomenon of water loss, any other desorption events at higher temperature could not be observed from the recorded thermogravimetric profiles.

TABLE 3 1e - TGA/DTGA 1d - TGA/DTGA T_(max) (° C.) 1c Total amount of for maximum water water desorbed rate of water Samples No desorption 35° C.-800° C. desorption S12 47.9 ± 0.33% 46.95 ± 0.57% 80.9 ± 1.6° C. S14 48.8 ± 0.03% 51.29 ± 0.06% 82.6 ± 1.2° C. S16 51.2 ± 0.13% 51.60 ± 0.50% 81.6 ± 2.8° C.

Example 2—Characterization of Support Composition

In this example a calcium phosphate (Ca/P) support labelled S97 was made under similar conditions as those described in example 1 of WO2015/173437 patent application. The sample was dried for 48 h at 105° C. in a drying oven. All analyses below have been carried on the dried sample.

The composition of the support was determined.

The calcium carbonate (CaCO₃) concentration was calculated from the following technique. An Orsat gas analyzer is an apparatus in which various gases, in this case CO₂, can be selectively absorbed by passing them through a series of preselected chemical solutions. The apparatus mainly consists of a calibrated water-jacketed gas burette, containing slightly acidified NaCl brine with a trace of a colour indicator (methyl orange). The burette is connected by glass capillary tubing to an absorption bottle containing a 4 M sodium hydroxide solution, which absorbs the CO₂ gas. By acidification and heating of the sample, carbonate is liberated as CO₂ gas. The volume of gas in the burette is read before and after absorption in the NaOH solution. The difference in volume corresponds to the CO₂ liberated from the sample. The quantity of carbonate is calculated from the volume of CO₂, taking the temperature of the water in the water-jacket of the burette into account as well as the atmospheric pressure.

The total calcium concentration was determined by potentiometric titration with EDTA solution using an indicative calcium electrode (ion selective electrode Ca²⁺ electrode Metrohm 6.0508.110) and an Ag/AgCl reference electrode (Metrohm 6.0726.100). During titration an electronic voltmeter can be used to detect the change in potential between the two electrodes. The equivalence point of the titration corresponds to the jump in voltage observed when all the Ca is complexed by EDTA. The indicative calcium electrode detects the disappearance of free (uncomplexed) calcium. The titrator was Metrohm 799 GPT Titrino.

Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine P and the minor elements Mg and Si. The magnesium carbonate (MgCO₃) concentration was calculated from the Mg concentration (measured by ICP-OES). The silicon dioxide (SiO₂) concentration was calculated from the Si concentration (measured by ICP-OES).

The water content was determined by colometric Karl-Fisher titration after thermal desorption at 300° C. The sample was heated in a dedicated tubular furnace for KF analysis and the desorbed water was swept by means of a dry argon gas flow into the colometric titration cell, containing the colometric Karl Fischer reagent (methanol, diethanolamine, sulfur dioxide, imidazole and imidazolium iodide).

The hydroxyapatite concentration was calculated from the Ca and P concentrations in the following way:

-   -   The molar Ca concentration to be assigned to hydroxylapatite was         calculated from the total % Ca concentration (determined by         potentiometric titration with EDTA solution) minus the calcium         already assigned to CaCO₃: 8.22 mol/kg     -   The molar P concentration assigned to hydroxyapatite was         calculated from the total % P concentration (measured by         ICP-OES): 5.19 mol/kg     -   Then the molar Ca/P ratio in the hydroxyapatite was calculated         from these molar Ca and P concentrations assigned to         hydroxyapatite. The estimated molar Ca/P ratio of the         hydroxyapatite was 1.58, whereas the theoretical Ca/P of         hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) is 1.67. Hydroxyapatites with a         molar Ca/P ratio between 1.50 and 1.67 are calcium-deficient         hydroxyapatite (CDA) with the chemical formula         Ca_(10-x)(HPO₄)_(x)(PO₄)_(6-x)(OH)_(2-x).     -   x has been calculated from the molar Ca/P ratio:         x=10-6*Ca/P=0.503.     -   Thus, the exact chemical formula of the calcium-deficient         hydroxylapatite was slightly different from the theoretical         hydroxylapatite chemical formula:         Ca_(4.497)(HPO₄)_(0.503)(PO₄)_(5.497)(OH)_(1.497) with a molar         mass of 976.41 g/mol.

The following TABLE 4 summarizes the estimated composition in wt % of the support sample S97. The sum of the compounds in the table above is slightly below 100% due to the experimental uncertainty associated with each of the analytical methods applied. The support contains no carbon.

TABLE 4 Concentration in Constituent wt % (calcium-deficient) hydroxyapatite- 84.5 Ca/P molar ratio = 1.58 calcium carbonate 9.1 Water 3.7 magnesium carbonate 0.8 silicon dioxide 0.3 Total 98.4 Absence of Calcium Dihydroxide (Ca(OH)₂) Demonstrated by pH Determination:

The support did not contain calcium dihydroxide (Ca(OH)₂). This absence of soluble hydroxide from calcium dihydroxide (Ca(OH)₂) was demonstrated by preparing a diluted sample suspension and by measuring the pH of the supernatant solution. Hydroxylapatite being extremely insoluble in water (K_(sp)=6.8×10⁻³⁷), the OH⁻ from the apatite molecule does not contribute to the pH. Calcium carbonate is also very insoluble (13 mg/l à 25° C.), whereas Ca(OH)₂ is soluble until 1.6-1.7 g/l at 20° C. If the pH of the sample solution is lower than 7, then the sample cannot contain any Ca(OH)₂. In order to demonstrate what the pH would be if the sample contained 0.1% calcium dihydroxide, the pH was also measured in a solution of a sample spiked with 0.1% calcium dihydroxide. The pH electrode was a calibrated Aquatrode Plus with Pt 1000 temperature sensor (Metrohm 6.0257.000).

-   -   Sample solution: 5 g of sample were brought into contact with         degassed ultrapure water at about 20° C. during 10 min while         stirring the liquid. The suspension was then centrifuged. At         this concentration of sample in the solution, up to 1.6% of         Ca(OH)₂ in the original solid sample would still be soluble. An         aliquot of the supernatant was then diluted about 3 times and         the pH was measured.     -   Solution of a sample spiked with 0.1% Ca(OH)₂: 5 g of         sample+0.005 g Ca(OH)₂ were brought into contact with degassed         ultrapure water during 10 min while stirring the liquid. The         suspension was then centrifuged. An aliquot of the supernatant         was then diluted about 3 times and the pH was measured.

The pH of the sample solution was 6.3. Since there is no alkalinity, there was no calcium dihydroxide in the sample. The pH of the sample spiked with 0.1% of calcium dihydroxide was 7.5. It was concluded that the support material did not contain calcium dihydroxide.

Example 3—Preparation of Catalysts

The catalyst samples prepared were identified by a code; in the code there were the Cu wt. % (X), the preparation method used (I: Impregnation or E: ion exchange), the Cu-precursor used (Ac: Acetate or Acac: Acetylacetonate or NO: nitrate or Cl: Chloride) and the support sample (S16 as used in Example 1).

3a—Examples of Catalyst Preparation by Impregnation

Catalyst Cu2IAcac/S16:

The support sample S16 was dried at 120° C. for 16 h=6.0549 g. 0.5042 g Cu(Acac) was dissolved in 150 ml of mixture water-isopropyl alcohol (1:1) (not clear solution) to reach a molar concentration of 0.016 M and put into contact with support sample.

1° step: Cu-deposition on S16 surface by using a rotary evaporator and a dropping-funnel, by alternating cycles of dropping of the Cu-solution and evaporation of the solvent (hot water maintained at 60° C.). The operation lasted 6 hours.

2° step: drying of the impregnated powder in an oven at atmospheric pressure at 120° C., 16 hours.

3° step: calcination: 1° C./min up to 450° C., maintained for 4 hours.

5.151 g of catalyst sample was obtained with a Cu content of 1.98 Cu wt. %.

Catalyst Cu2IAc/S16:

The support sample S16 was dried at 120° C. for 16 hours=6.049 g. 0.4060 g Cu(Ac) was dissolved in 20 ml water to reach a molar concentration of 0.108 M and put into contact with support sample.

1° step: Cu-deposition on S16 surface by using a rotary evaporator and a dropping-funnel, by alternating cycles of dropping of the Cu-solution and evaporation of water (hot water maintained at 80° C.). The operation lasted ca. 4-5 hours.

2° step: drying of the impregnated powder in an oven at atmospheric pressure at 120° C., 16 hours. 3° step: calcination: 1° C./min up to 450° C., maintained for 4 hours.

5.286 g of a catalyst sample was obtained with a Cu content of 2.089 Cu wt. %.

3.b Example of Catalyst Preparation by Ion Exchange

Catalyst Cu8EAc/S16

Support S16 dried at 120° C., 16 h=5.9819 g

Cu(Ac): 2.4837 g was dissolved in 250 ml water to reach a molar concentration of 0.0497 M.

1° step: Addition of S16 powder into the clear solution of Cu(Ac) under vigorous magnetic stirring at 40° C. (pH=7), the operation lasted 20 hours.

2° step: Separation of the solid from the solution by filtration under moderate vacuum (ca. 15 mbar); measurement of the absorbance of the filtrate waters to compute the residual Cu(Ac) concentration.

3° step: washing cycles with hot water (40° C.) up to the obtainment of clear water without any Cu(Ac) amount.

4° step: drying of the exchanged powder in an oven at atmospheric pressure at 120° C., 16 hours

5° step: calcination, 1° C./min up to 450° C., maintained for 4 hours.

Catalyst sample obtained g=5.546 (8.23 Cu wt. %)

Four more catalysts were prepared in a similar manner by ion exchange with 1.5 wt %, 3 wt %, 6 wt % and 11 wt % using copper acetate as Cu precursor and identified as Cu1,5EAc/S16, Cu3EAc/S16, Cu6EAc/S16, Cu11EAc/S16.

Catalyst Cu6ENO/S16 (Dried; not Calcined)

Support: S16 dried at 120° C., 16 hours=5.123 g

Cu(NO3)2: 1.141 g was dissolved in water, 250 ml to reach a molar concentration of 0.024 M.

1° step: Addition of S16 powder into the clear solution of Cu(NO₃)₂ under vigorous magnetic stirring at 40° C. (pH=7), the operation lasted 20 hours.

2° step: Separation of the solid from the solution by filtration under moderate vacuum (ca. 15 mbar); measurement of the absorbance of the filtrate to compute the residual Cu(NO₃)₂ concentration.

3° step: washing cycles with hot water (40° C.) up to the obtainment of clear water

4° step: drying of the exchanged powder in an oven at atmospheric pressure at 120° C., 16 hours

Catalyst sample obtained g=5.075 (6.59 Cu wt. %)

Example 4—SCR Testing of Catalysts

4a. Preparation of Catalyst Loading into SCR Reactor.

A continuous flow reactor was part of the Selective Catalytic Reaction system. When using such a flow reactor, the catalyst sample has to be put inside as grains of given size; placing solids in powder form would result in high pressure loss, with consequences of having non-correct fluid dynamics when feeding gaseous mixture. The dimension of the grains has to be selected so as to guarantee the absence of diffusional limits (external and internal diffusion) and a suitable fluid dynamics of the gaseous mixture.

For that reason, the catalyst samples to be tested were pressed, crushed, and sieved as particles of 45-60 mesh (0.354 mm-0.250 mm, respectively) in size. The procedure to realize such particles was not straightforward as the correct pressure had to be found experimentally in order to obtain catalyst grain sizes stable to mechanical shocks; the grains should not lose powder with time during the reaction.

For hydroxyapatite-based Cu catalyst samples tested for SCR reaction, the grains were obtained by pressing each powder sample put between two steel disks under 3 tons for 30 seconds. The resulting sample in form of compacted disk (of few mm thickness) was then crushed and sieved between two sieves of 45 and 60 mesh (0.354 mm-0.250 mm, respectively) of size.

4b. NH₃-SCR Reaction Experimental Procedure.

Tests of the SCR reaction were performed in a continuous reaction line equipped with a set of mass flow controllers (Bronkhorst, Hi-Tec and Brooks Instruments), a tubular vertical electric oven (maximum temperature of 1000° C.), a glass tubular catalytic micro reactor (with 5 mm i.d.), and an on-line FTIR spectrophotometer (Bio-Rad with DTGS detector) for the qualitative and quantitative determination of the fed and vented gaseous species.

A catalyst sample (ca. 0.20 g), sieved as particles of 0.35-0.25 mm of size and dried at 120° C. in an oven overnight, was pre-treated in situ under an O₂/He flow (20% v/v) at 120° C. for 30 min.

Typically, when the catalyst activity was studied for a given temperature selected to be in the 120-400° C. range, the concentration of the feeding gas mixture and total flow rate were maintained constant via a Eurotherm Controller-Programmer type 818, and the temperature at which the reaction was being studied was maintained at least for 60 minutes in order to allow reaching steady-state conditions.

Typically, the fed gas mixture was prepared mixing ca. 500 ppm of NO, 500 ppm of NH₃, and 10,000 ppm of O₂. After the mixing, the effective gas mixture being fed to the catalyst bed also contained NO₂ (formed from the reaction in gas phase between NO and O₂): ca. 450 ppm of NO, 50 ppm of NO₂, 500 ppm of NH₃, and ca. 10,000 ppm of O₂. The total flow of the gaseous mixture was kept constant at 6 NL/h (corresponding to 0.12 s of contact time).

The mixture exiting from the reactor was monitored each 180 seconds by FT-IR equipped with a multiple reflection gas cell with 2.4 m path length; resolution, 2 cm⁻¹; sensibility, 1.5, 92 scans per 180 seconds) for quantified the reagent species. The total absorbance of all the IR active species (Gram-Schmidt) flowing from the reactor was continuously monitored as a function of time, while the reaction temperature was changing. The NO, NO₂, and NH₃ and other formed species (if any) were quantified from the peak height of a selected absorbance lines, on the basis of the measured calibration factors.

The following TABLE 5 provides the working wavelengths (cm⁻¹) for the IR active species NO, NO₂, N₂O, NH₃, H₂O:

TABLE 5 Species NO NO₂ N₂O NH₃ H₂O IR working 1875.99 1626.40 590 966 1580 wavelengths (cm⁻¹)

4c. NH₃-SCR Catalytic Tests: Experimental Results with Support S16/400/8

As a control, the NH3-SCR reaction on the hydroxyapatite-based support (S16/400/8, calcined at 400° C. for 8 hours) was studied over the range of temperature 120-450° C. while the concentration of the feeding mixture and flow rate were maintained the same (that is to say the contact time remained the same). The sample was prepared as explained in the Section 4.a. The sample was pre-treated under a flow of O₂ in He (20%) at 3 NL/h for 30 min at 120° C. The feeding mixture contained NO, NH₃, O₂, as well as NO₂ formed in gas phase from NO+O₂.

Conditions for the Reaction Test:

Flow 6 (NL/h) Surface Area 92.76 (m²/g) Cat. Density 1 (g/ml) Cat. Mass dry 0.198 (g) GHSV 30272 (h⁻¹) Contact Time (t1) 3.303E−05 (h) Contact Time (t2) 119 (g * s/NL) Contact Time (t3) 2.665 (g * s/mmol)

From the concentration values of all the species involved in the SCR reaction, the catalytic data can be computed. FIG. 1 illustrates the conversion of NO and NH3 over the hydroxyapatite-based support S16/400/8 over the range of temperature 120-450° C. Conversion of NO was around 15-20% and that of NO₂ was much higher (ca. 60-70%); the reactivity of NO₂ is much higher than that of NO. Ammonia, after being adsorbed at low temperature (120° C.), had conversion around 20-30% in the temperature range 200-450° C. These observations showed that S16/400/8 support sample was inert in the NH₃-SCR reaction.

4d. NH₃-SCR Catalytic Tests: Experimental Results with Two Catalysts Over Temperature Range

The NH3-SCR reaction was studied on two catalysts prepared by ion-exchange on the same support S16 with copper acetate as a precursor (Cu1.5EAc/S16 and Cu11EAc/S16) over the range of temperature 120-400° C. while the concentration of the feeding mixture and flow rate were maintained the same (that is to say the contact time remained the same). The catalyst samples were made as explained in the Section 3b; their actual Cu contents were 1.725 wt % Cu and 11.14 wt % Cu. The catalyst samples were prepared and loaded in the SCR reactor as explained in the Section 4a. The catalyst sample was pre-treated under a flow of O₂ in He (20% v/v) at 3 NL/h for 30 min at 120° C.

Conditions for the Reaction Test with Cu1.5EAc/S16:

Flow 6.01 (NL/h) Cat. Density 1 (g/ml) Cat. Mass 0.178 (g) GHSV 33688 (h⁻¹) Contact Time (t1) 2.968E−05 (h) Contact Time (t2) 107 (g * s/NL) Contact Time (t3) 2.395 (g * s/mmol) PM_(CuO) 79.55 (g/mol) % Cu 1.725 Conditions for the Reaction Test with Cu11EAc/S16:

Flow 6 (NL/h) Cat. Density 1 (g/ml) Cat. Mass 0.212 (g) GHSV 28355 (h⁻¹) Contact Time (t1) 3.527E−05 (h) Contact Time (t2) 127 (g * s/NL) Contact Time (t3) 2.846 (g * s/mmol) PM_(CuO) 79.55 (g/mol) % Cu 11.14

The percent conversion of NO and NH₃ and the percent of production of N2 as a function of the reaction temperature are provided in FIGS. 2 and 3 over the hydroxyapatite-based Cu catalysts: Cu1.5EAc/S16 and Cu11EAc/S16, respectively, over the range of temperature 120-400° C.

For Cu11EAc/S16: the conversion of NO attained a maximum (ca. 36%) at 250° C. The production of N₂ is largely higher than the NO conversion because N₂ can be formed by both the reaction of NO reduction by NH₃ and by NH₃ oxidation by O₂. The production of N₂ decreases at high temperatures of reaction because other species (N₂O, NO, and NO₂) are formed from NH₃ oxidation by O₂.

For Cu1.5EAc/S16: the conversion of NO had not a clear increasing trend, a certain increase of conversion was detectable up to 200° C. and then it was maintained on similar values; at the highest reaction temperatures, the NO conversion increased, likely due to the NO formation by the NH₃ oxidation by O₂. Ammonia conversion attained 100% starting from 275° C.

It was found that the curve describing the N₂ production with temperature was interesting for Cu1.5EAc/S16, as it was continuously increasing with different slopes in the different ranges of temperature. At low reaction temperature, the N₂ formation increased with high slope, then, the N₂ formation was quite constant and for the highest temperatures it had a new increase of slope. The trend suggests that at low temperature, N₂ comes from the NO reduction and at the highest temperatures, N₂ comes from the NH₃ oxidation by O₂.

On this lower-loading catalyst, the competitive reaction of ammonia oxidation by oxygen did not seem very active and highly oxidized products such as N₂O and NO₂ were not observed, contrary to what was observed with the much-higher Cu loaded catalyst Cu11EAc/S16.

It seems that the loading of copper on the hydroxyapatite-based support (here S16) could alter the selectivity of the two reactions: oxidation of NH₃ by NO with formation of N₂ (see reaction I) and the various oxidation reactions of NH₃ by O₂ with formation of NO, N₂O, N₂ (see reactions V, VI, VII).

4e. NH₃-SCR Catalytic Tests: Experimental Results with Copper Exchanged Catalysts

Seven copper catalysts at different Cu(II) concentration have been prepared by ionic exchange starting from different Cu-precursors and at different Cu concentrations (1.7<Cu (wt. %)<11.1): five catalysts made with copper acetate as a precursor (1.7<Cu (wt. %)<11.1), labeled Cu1.5EAc/S16, Cu3EAc/S16, Cu6EAc/S16, Cu8EAc/S16, and Cu11.2EAc/S16 with their actual Cu loadings being 1.725 wt % Cu, 2.761 wt % Cu, 6.041 wt % Cu, 8.228 wt % Cu, and 11.14 wt % Cu; one catalyst made with copper nitrate (6.59 Cu wt. % Cu) labeled Cu6ENO/S16; and one catalyst made with copper chloride (6.09 wt. % Cu) labeled Cu6ECl/S16. In their preparation, these catalysts were calcined at 400° C.

N₂ adsorption and desorption isotherms (at −196° C.) on the copper catalysts were performed to evaluate the morphological properties of all the catalyst samples. Specific surface area was computed by interpreting the adsorption isotherms (in the interval of relative pressure: 0.033<P/Po<0.35) with the linear BET equation. Pore Volume was determined as converting all the amount of N₂-gas adsorbed (cm³/g) at P/Po=0.99 to N₂-liquid (cm³liq/g). Pore size and pore size distribution were determined by interpreting the desorption branch of the N₂ adsorption/desorption isotherms with the BJH (Barrett-Joyner-Halenda) model equation (extension of Kelvin equation). Average pore size (rav,p, pore radius in nm) was calculated by the classical Gurvitch's rule, which assumes cylindrical shape of the pores: rav,p(Å)=(2 VP/SBET) 10⁴ or rav,p(nm)=(2 VP/SBET) 10³. Prior to the analysis, the dried and weighted samples (ca. 0.2 g) have been outgassed at 150° C. for 4 hours under vacuum. The morphological properties (specific surface area, pore volume, pore size and pore size distribution) for the prepared Cu-exchanged catalysts are listed in TABLE 6.

TABLE 6 Copper catalysts prepared by ion exchange on S16 Average Cu- Cu- Surface Pore Pore pore pre- loading Area^(a) Volume^(b) radius^(c) radius^(d) Sample cursor Wt % (m²/g) (cm³/g) (nm) (nm) S16 92.7 0.690 — 15 Cu1.5EAc/ CuAc 1.72 75. 0.484 1-6 12.5 S16 Cu3EAc/S16 CuAc 2.76 83.5 0.470 2-8 11.2 Cu6EAc/S16 CuAc 6.04 79.1 0.749 2-8 18.9 Cu8EAc/S16 CuAc 8.22 84.1 0.549 2-8 13.1 Cu11EAc/ CuAc 11.14 97.4 0.567 2-9 11.6 S16 Cu6ENO/ CuNO 6.59 81.4 0.312 2-7 7.67 S16 (calc.) Cu6ENO/ CuNO 6.59 93.4 0.541 2-7 10.8 S16 (dry) Cu6ECl/ CuCl 6.09 78.3 0.636 — — S16 ^(a)determined from 2-parameters BET equation ^(b)determined at P/Po = 0.99 ^(c)observed from PSD (by BJH model from desorption branch of the isotherm) ^(d)determined from Gurvich-rule: rp (nm) = (2 Vp/SBET) · 10 with Vp in cm³/g and SBET in m²/g

For all of these ion-exchanged catalyst samples, the particle size distribution was broad; and the morphology of the materials was microporous and mesoporous.

XRD analysis showed that the ion-exchanged catalyst samples had a crystalline structure matching that of the hydroxyapatite (HAP) typical XRD pattern found in JCPDS: 00-009-0432.

For the Cu-exchanged catalysts, the BET surface area was comprised in the range of 75-98 m²/g; it seems that the BET values increased with the Cu content, supporting the formation of nanoaggregates of CuO at the external surface of the support (S16). In general, the surface area values were slightly lower than that of the (non-loaded) S16 support (92.7 m²/g measured after calcination at 400° C.; 15 nm in av. pore radius). There was no significant modification of the computed BET values by increasing the Cu concentration on the catalyst. This indicated a good distribution of Cu species on the S16 support. For the Cu-exchanged catalysts, the pore volume was comprised in the range of 0.312-0.749 cm³/g (compared to 0.69 cm³/g pore volume measured after calcination at 400° C. for the support S16).

The NH₃-SCR reaction was studied for these seven catalysts prepared by ion-exchange on the same support S16 at a given temperature of 250° C.—the concentration of the feeding mixture and flow rate were maintained the same (that is to say the contact time remained the same). The catalyst samples were prepared and loaded in the SCR reactor as explained in the Section 4a. The catalyst sample was pre-treated under a flow of O₂ in He (20% v/v) at 3 NL/h for 30 min at 120° C.

The percent conversion of NOx obtained with a NH₃:NO molar ratio of 0.82 are provided in FIG. 4 over the 7 hydroxyapatite-based Cu catalysts over the given temperature of 250° C. with:

-   -   a NH₃:NO molar ratio of 0.82,     -   a contact time of 3.01 10⁻⁵ hour,     -   an O₂ concentration of 10,000 ppm and     -   an initial NO concentration of about 550 ppm.

FIG. 4 reports the comparative results for the DeNOx activity at temperature of 250° C. of the 7 Cu-catalysts prepared by ionic exchange with Cu loadings on hydroxyapatite support from 1.7 to 11.1 wt. % Cu (Conditions: NOx=580 ppm; NH3=500 ppm; 02=1%; GHSV=30,000 h⁻¹; catalyst=0.2 g).

If copper acetate was used as precursor of the copper phase deposited via ion-exchange, a Cu-content around 3-6 wt. % Cu3EAcS16 and Cu6EAc/S16 seemed representing the optimal Cu concentration for obtaining active deNOx catalysts. The catalysts attained good conversion of NO (they were active in the NH₃-SCR of NOx) and they did not suffer as much from the competitive reaction of NH3 oxidation by O₂ with formation of NO, N₂O, N₂ (via reactions V, VI, VII). Further addition of Cu did not improve the NOx conversion attained.

Quite surprisingly though, the catalysts prepared from Cu(NO₃)₂ and CuCl₂ precursors (Cu6ENO/S16, Cu6ECl/S16) gave much higher NOx conversion comparing with the catalysts prepared with copper acetate precursor Likely, the double ionic nature of the anion (NO³⁻ and Cl⁻) and cation (Cu²⁺) of the Cu-salt precursors could modify the hydroxyapatite surface involving also the PO₄ ³⁻ sites that can be substituted with the entered anions, this likely led to positive consequences on deNOx activity.

FIG. 5 reports the comparative results for the DeNOx activity at temperature of 350° C. of the same 7 Cu-catalysts prepared by ionic exchange with Cu loadings on hydroxyapatite support from 1.7 to 11.1 wt. % Cu (Conditions: NOx=580 ppm; NH3=500 ppm; 02=1%; GHSV=30,000 h⁻¹; catalyst=0.2 g). All Cu catalysts prepared by ionic exchange from copper acetate showed a decrease of activity at 350° C. in comparison with the activity shown at 250° C. (FIG. 4). This corresponds to the typical trend of the most part of deNOx catalysts reported in the open literature. The catalysts prepared from copper salt (nitrate, chloride) precursors (Cu6ENO/S16 and Cu6ECl/S16) were highly selective, their deNOx activity did not decrease significantly at 350° C. in comparison with that measured at 250° C.

4f. NH₃-SCR Catalytic Tests: Experimental Results with Copper Impregnated Catalysts

Six copper catalysts at different Cu(II) concentration have been prepared by impregnation starting from different Cu precursors and at different Cu concentrations (2.1<Cu (wt. %)<10.1): four catalysts made with copper acetate (2.1<Cu (wt. %)<10.1) labeled Cu2IAc/S16, Cu6IAc/S16, Cu8IAc/S16, and Cu10IAc/S16, one catalyst made with copper nitrate (6.1 Cu wt. %) labelled Cu6INO/S16; and one catalyst made with copper acetylacetonate (2.0 wt. % Cu) labeled Cu2IAcac/S16.

N2 adsorption and desorption isotherms (at −196° C.) on the copper catalysts were performed to evaluate the morphological properties of all the catalyst samples as described above in Example 4e. The morphological properties (specific surface area, pore volume, pore size and pore size distribution) for the prepared Cu-impregnated catalysts are listed in TABLE 7.

TABLE 7 Copper catalysts prepared by impregnation on S16 Average Cu- Cu- Surface Pore Pore pore pre- loading Area^(a) Volume^(b) radius^(c) radius^(d) Sample cursor Wt % (m²/g) (cm³/g) (nm) (nm) S16 92.7 0.690 — 15 Cu2IAc/S16 CuAc 2.09 85.0 0.518 2-8 12.2 Cu6IAc/S16 CuAc 5.77 73.4 0.784 2-8 21.4 Cu8IAc/S16 CuAc 7.79 67.8 0.800 — — Cu10IAc/ CuAc 10.09 66.2 1.101 — — S16 Cu2IAcac/ CuAcac 1.98 76.4 0.702 — — S16 Cu6INO/S16 CuNO 6.10 79.8 0.814 — — ^(a)determined from 2-parameters BET equation ^(b)determined at P/Po = 0.99 ^(c)observed from PSD (by BJH model from desorption branch of the isotherm) ^(d)determined from Gurvich-rule: rp (nm) = (2 Vp/SBET) · 10³ with Vp in cm³/g and SBET in m²/g

For all of these impregnated catalyst samples, the particle size distribution was broad; and the morphology of the materials was microporous and mesoporous.

XRD analysis showed that the impregnated catalyst samples had a crystalline structure matching that of the hydroxyapatite (HAP) typical XRD pattern found in JCPDS: 00-009-0432 as well as the XRD pattern found for CuO JCPDS: 048-1548 pattern (from literature).

For the Cu-impregnated catalysts, the BET surface area was comprised in the range of 66.2-85 m²/g, slightly lower than that of the (non-loaded) S16 support (92.7 m²/g measured after calcination at 400° C.). For the Cu-impregnated catalysts, the pore volume was comprised in the range of 0.52-1.1 cm³/g (compared to 0.69 cm³/g pore volume measured after calcination at 400° C. for the support S16).

Comparison of deNOx activity of all the catalysts prepared by impregnation at different Cu concentrations and prepared from various Cu precursors (copper acetate, copper nitrate, and copper chloride) is reported in FIG. 6 at temperature of 250° C. (Conditions: NOx=580 ppm; NH₃=500 ppm; O₂=1%; GHSV=30,000 h⁻¹; catalyst=0.2 g). In this case, the NOx conversion observed at 250° C. was much higher (70-80%) than that shown by the catalysts prepared by ionic exchange. The catalyst activity was quite the same independently of the Cu loading and of the nature of Cu precursor.

The deNOx activity of Cu2IAcac/S16 (the sample prepared from acetylacetonate precursor) was very high. This result was surprising because the preparation of the support sample was challenging, due to solubility problems of the precursor both in water and in several organic solvents. Even though there was some issue with the catalyst preparation which likely resulted in not an homogeneous dispersion of Cu phase on the hydroxyapatite support, the observation of high deNOx activity (despite the likely poor Cu dispersion) indicated that the NOx reductions required the presence of aggregates of CuOx on the surface.

FIG. 7 reports the comparative results for the deNOx activity at temperature of 350° C. of the same 5 Cu-catalysts prepared by impregnation with Cu loadings on hydroxyapatite support (2.1<Cu (wt. %)<10.1). Conditions: NOx=580 ppm; NH₃=500 ppm; 02=1%; GHSV=30,000 h⁻¹; catalyst=0.2 g.

4g. NH₃-SCR Catalytic Tests: Impact of Method of Preparation of Catalysts

Two catalysts at the same Cu loading on S16 support (Cu6IAc/S16 and Cu6EAc/S16) were prepared by the 2 different methods of Cu deposition (ion exchange vs. impregnation) as described above in sections 3a and 3b. They were compared towards their deNOx activity (see FIG. 8). FIG. 8 shows that the Cu presence was necessary for the deNOx activity at low temperatures (150-300° C.) and that impregnation seemed a better preparation method than ionic exchange method when copper acetate was used as Cu precursor.

For comparison purposes, deNOx activity of the two catalysts prepared on a chabazite (“HCZC”) support by ion exchange and impregnation at similar copper loading of 2 wt % Cu (Cu2EAc/HCZC and Cu2IAc/HCZC). In this case, it was observed that the preparation method did not influence very much the performances of the obtained catalysts. Both the catalysts had good deNOx activity in a wide range of temperatures.

4h. NH₃-SCR Catalytic Tests: Impact of Cu Precursor on Catalyst's Activity

The NOx conversion was measured as a function of reaction temperature for the catalysts prepared by ion exchange for a given with different copper precursors (Cu6EAc/S16; Cu6ECl/S16; Cu6ENO/S16) over a range of temperatures (120-400° C.). The data is illustrated in FIG. 9.

FIG. 9 indicates that there was a variation between the catalyst samples prepared from Cu-acetate, Cu-nitrate, and Cu-chloride. The catalysts prepared starting from copper nitrate and copper chloride precursors showed very similar behavior of their catalytic performances in the deNOx reaction. Their activities are both higher than that observed on Cu6EAc/S16 (catalyst prepared from Cu-acetate precursor). The most important difference among the three catalysts was in their catalytic behavior at high temperature (>250° C.): Cu6ENO/S16 and Cu6ECl/S16 maintain good deNOx activity, with only slight decrease of NOx conversion. It emerges that Cu6ENO/S16 had the best activity, also better than that observed on Cu6ECl/S16.

From FIG. 9, it seems that the ionic salts used as Cu-precursors (Cu-chloride and Cu-nitrate) gave rise to very similar deNOx activity. 

The invention claimed is:
 1. A porous material or support comprising at least 60 wt % of a calcium-deficient hydroxyapatite having a calcium to phosphate molar ratio (Ca/P) of less than 1.67, said porous support having a specific BET surface area of at least 110 m²/g and a pore volume of at least 0.41 cm³/g, both measured after heat treatment at 120° C.
 2. The porous material or support according to claim 1, further comprising calcium carbonate in an amount of less than 20 wt % and more than 0 wt %.
 3. The porous material or support according to claim 1, comprising less than 1 wt % of calcium dihydroxide Ca(OH)₂.
 4. The porous material or support according to claim 1, further comprising water in an amount of less than 20 wt % and more than 0 wt %.
 5. The porous material or support according to claim 1, comprising a Ca/P molar ratio of 1.60 or more.
 6. The porous material or support according to claim 1, comprising a Ca/P molar ratio greater than the Ca/P molar ratio of the calcium-deficient hydroxyapatite.
 7. The porous material or support according to claim 1, comprising at least 65 wt % of the calcium-deficient hydroxyapatite, and/or comprises at most 99 wt % of the calcium-deficient hydroxyapatite.
 8. The porous material or support according to claim 1, having a BET specific surface area measured after heat treatment at 400° C. of at least 60 m²/g and/or at most 100 m²/g.
 9. The porous support according to claim 1, having a pore volume measured after heat treatment at 200° C. of at least 0.5 cm³/g and/or at most 1.0 cm³/g.
 10. The porous material or support according to claim 1, having a pore volume measured after heat treatment at 400° C. of at least 0.50 cm³/g and/or of at most 1 cm³/g.
 11. A catalyst composition for catalytic reduction of NO_(x) compounds, comprising an active catalyst component deposited on the porous material or support according to claim 1, wherein said active catalyst component comprises copper, copper oxide, or combination thereof.
 12. The catalyst composition according to claim 11, wherein the active catalyst component comprises at least 0.1 wt % of copper, copper oxide, or combination thereof; and/or at most 15 wt % of copper, copper oxide, or combination thereof.
 13. The catalyst composition according to claim 11, wherein the active catalyst component is deposited on the porous support by ion exchange.
 14. The catalyst composition according to claim 11, wherein the active catalyst component is deposited on the porous support using a copper precursor selected from the group consisting of copper nitrate, copper acetate, copper chloride, copper acetylacetonate, and any mixture thereof.
 15. The catalyst composition according to claim 11, wherein the catalyst is subjected to a heat treatment using a temperature from 105° C. up to 500° C., prior to being used as a catalyst.
 16. The catalyst composition according to claim 11, wherein the catalyst composition has a BET specific surface area measured after being calcined at 400° C. of at least 65 m²/g and/or at most 100 m²/g.
 17. The catalyst composition according to claim 11, wherein the catalyst composition has a pore volume measured after being calcined at 400° C. of: at least 0.3 cm³/g, and/or at most 1.1 cm³/g.
 18. A process for treating a waste gas stream containing nitrogen oxides (NOx), said gas stream originating from a combustion process, wherein an ammonia source is injected into the waste gas stream; and wherein the catalyst composition according to claim 11 is brought into contact with the waste gas stream containing ammonia at a temperature of at least 100° C. and at most 600° C. to carry out, in the presence of O₂, a reduction by NH₃ of at least a portion of the NOx to N₂ and water.
 19. The process according to claim 18, wherein the waste gas stream temperature is at least 105° C. and/or at most 550° C.
 20. The process according to claim 18, wherein the catalyst composition is injected into the waste gas stream in the form of a dry powder injection or a semi-dry injection of a slurry of the catalyst. 